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In the later years of his life Leonardo da Vinci described the configuration of the earth’s crust as the result of actual processes, principally fluvial, operating over immense periods of time—a system of geology which Duhem described as “perhaps his most complete and lasting invention” (Duhem, II, p.342).

For Leonardo , the study of the great world was related to the study of man. “Man is the model of the world” (Codex Arundel, fol. 156v; De Lorenzo, p.8), he wrote, “-called by the ancients a microcosm..., composed like the earth itself, of earth, water, air and fire; as man contains within himself bones, the supports and armature of the flesh, the world has rocks, the supports of the earth’s; as man has in him the lake of blood which the lungs swell and decrease in breathing, the body of the earth has its oceanic sea which also swells and diminishes every six hours in nourishing the world” (MS A fol. 55v).

Leonardo’s geologic perceptions date back to his earliest apprenticeship in Florence. Horizontally stratified rocks in the foreground and pyramidal peaks above a background sea in the Baptism of Christ (Uffizi, Florence), which he worked on with his master Verrocchio in 1472, reflect the influence of Van Eyck on Florentine landscape conventions (Castelfranco, p. 472).

Leonardo’s earliest dated work (1473), probably drawn in the field, is a sketch of the valley of the Arno (Uffizi). It displays similar characteristics-horizontal strata with waterfalls in the right fore ground, and eroded hills above a broad alluvial valley behind.

In subsequent drawings and paintings, rocks may be thrown into cataclysmic contortions but at the same time are folded and fractured realistically. (Leonardo’s infrequent mentions of earthquakes [Codex Leicester, fol. 10v], volcanoes [codex Arundel, fol. 155r; and Richter, 1939], and internal heat betray a lack of firsthand familiarity with Italy from Naples south. His idea of catastrophe was of storm, avalanche, and flood, and his apocalyptic essays do not alter the essential actualism of his system. He pointedly neglects the plutonist orogenic ideas of Albertus Magnus for the gradualist-neptunism of Albert of Saxony [Duhem, II, p.334].) The cliffs rising from a harbor in the background to the Annuciation (Uffizi) are not unlike views from above Lake Como or Lake Maggiore in the gathering mists. But the ultimate expression of Leonardo’s visual apprehension of topography and the true measure of the extent of his journey from the first sketch of 1473 is in the Windsor drawings of the Alps above the plains of the Po (Windsor Collection, folios 12410, 12414). They were done in the final years of his life in Italy at about the same time that he formulated his geologic notes in Tuscany before his Alpine studies). In these notes Leonardo boldly rejected Judeo-christian cosmology for the secular naturalism of the classical tradition as demonstrated by natural processes and by the actual configuration of the material world. Leonardo estimated that 200,000 years were required for the Po to lay down its plain ([Muentz, p.34]; he had clearly abandoned the JudeoChristian time scale for one that was two to three orders of magnitude greater [cf. Duhem, II, p. 335; and Richter, p. 915]).

In Leonardo’s system, the highest peaks of the Alps and the Apennines were former islands in an ancient sea. Mountains are continually eroded by winds and rains. Every valley is carved by its river, which is proven by the concordance of the stratigraphic column across the valley walls (codex Leicester, fol. 10r) and the proportionality of river size to valley breadth (Codex Atlanticus fol. 321b). The foothills and plains made by alluvial deposition continually extend the area of land at the expense of the sea. Mountains made lighter by erosion rise slowly to maintain the earth’s center of gravity at the center of the universe, bringing up petrified marine strata with their accompanying fauna and flora to be eroded into mountains in their turn.

Such great lakes as the Black Sea are impounded by the collapse of mountains and then, as streams breach the barriers, they drain down one into the other. In this way the Arno was seen to be cutting through its own flood plain, the Po to have filled in the great north Italian triangle from the Alps and Apennines to Venice, and the Nile from Memphis to Alexandria. The Mediterranean itself, the “greatest of rivers,” is being filling by the expanding deltas of its tributaries. When the future extension of the Nile erodes through the barrier of the Pillars of Hercules, it will drain what remains of the Mediterranean. Its bottom, relieved of the weight of the superincumbent sea, will rise isotatically (not to be confused with the modern concept of isotasy) to become the summits of mountains.

Just as Leonardo turned to dissection to study anatomy, so he dissected the earth—first in Milan during the years that he spent with Ludovico Sforza (il Moro); later as architect and engineer-general to Cesare Borgia and in land reclamation in Tuscany and for Leo X—for a period of 33 years from 1482 until 1515. Excavations for canals, moats, and roadways in Lombardy, Tuscany, Emilia, and the Romagna were carried out under his direct supervision during most of his career. He constructed plans and relief maps requiring exact measurements as well as lithologic and structural insight. His designs for surveying and drafting instruments; his numerous sketches, notes, and calculations of costs, manpower, and time; and his meticulous plans of machines for excavation and hydraulic controls all attest to the extent of his occupation with practical geology. The maps themselves- “bird’s—eye” topographic constructions, releif maps, and outline plans of drainage and culture are the geological analogues of his anatomical drawings, transcending sixteenth—century technics and science.

Leonardo was familiar with classical geological traditions through the works of Albertus Magnus and Cecco d’Ascoli, Vincent of Beatuvias, Ramon Lull, Isidore of Seville, Jan de Mandeville, and, above all, Albert of Saxony. Yet his demonstrations of the organic origins of fossils in situ, the impossibility of the biblical deluge, and the natural processes of petrifaction are based on meticulous observations—for example, of growth lines on shells (Codex Leicester, fol. 10a; Richter, p,990).

“When I was casting the great horse at Milan...,” he wrote, “Some countrymen brought to my workshop a great sack cockles and corals that were found in the mountains of Parma and Piacenza” (Codex leicester, fol. 9v). Was it his experience with the process of casting that led him ultimately to discuss the origins of the fossils and their cssts; of worm tracks;glossopetrae; fragmented and complete shells; paired and single shells; leaves; tufa; and conglomerates? Did this casting experience lead to a discussion of the relationship of velocity of flow to the sedimentary gradation from the mountains to the sea, of coarse gravels and breccias to the finest white potter’s clay?

Leonardo also observed and discussed turbidity currents (Codex Leicester, fol. 20r); initial horizontality (MS F, fol 11v); the relationship of sedimentary textures to turbulence of flow, graded bedding, the formation of evaporites of folded stara with mountains (Codex Arundel, fol.30b, Richter, 982).After numerous false starts, he arrived at an understanding of the hydrologic cycle (MS E, fol. 12a and Richter, 930); he dismissed the Pythagorean identification of the forms of the elements with the Platonic solids (MS F and Richter, 939); and he recorded the migration of sand dunes (MS F, fol. 61a and Richter, 1087).

After the period as engineer with Cesare Borgia, Leonardo had returned to Florence, then proceeded to Rome, and finally found sanctuary in Milan in 1508. Here he made the geologic notes of MS F under the heading De mondo ed acque. it is from this period also that the red chalk Windsor drawings of the Alps date, reflecting his interest in, and excursions into, the nearby Alps (Clark, p.134).

Leonardo brought not only his experience and his scientific principles to his landscapes, but also his sense of fantasy (Castelfranco, p. 473). The foreground of the two versions of the Virgin of the Rocks (Louvre and National Gallery) appears to be alternately horizontal, vertical, and horizontal strata, with caves widening into tunnels so that the roofs form natural bridges, some of them falling in. Such hollowing out from underneath and falling in of the back is the same mechanism used by Nicholas Steno in his Prodromus of 1669 to account for the inclination of strata.

Duhem has argued cognetly that Leonardo’s ideas were transmitted through Cardano and palissy to the modern world. There are many similarities which suggest a connection also with the highly influential Telliamed of Benoit de Maillet (1749). The notebooks were in part accessible well in advance of the modern development of a natural geology. G.B. Venturi’s studies of the geologic material in the notebooks were published in 1797 when catastrophic views of earth history were dominant. This was the year of birth of Charles Lyell, whose Principles of Geology in 1830 first formally established actualism as geologic orthodoxy. ( In later editions of the Principles, Lyell wrote that his attention was called to the Venturi studies by H.Hallam. G. Libri’s notes on Leonardo’s geology also date to the decade of Lyell’s principles. By contrast, the diluvial doctrine which Leonardo had demolished was seriously defended by William Buckland in his Reliquiae diluviianae as late as 1823, and catastrophism persisted well into the second half of the nineteenth century.)

Unfortunately, Leonardo rarely if ever sketched an indubitable fossil. He discussed but never illustrated the vivid Lake Garda ammonitico rosso—a Jurassic red marble with striking spiral ammonites used extensively in Milan. Leonardo’s realistic strata, especially in the Virgin and St.Anne of the Louvre, closely resemble these limestones as they weather in the Milanese damp. How is it possible that his “ineffable left hand” traced no illustrations of his comments—those comments which in their freshness, their simplicity, and vivid detail are a warranty of firsthand observation and an actualistic geologic position not achieved again for centuries? “The understanding of times past and of the site of the world is the ornament and the food of the human mind,” he wrote (Codex Atlantieus, fol. 365v).

Cecil J. Schneer


Arbitrary Collections
1. Codex Atlanticus1478–1518
2. Windsor Collection1478–1518
3. Codex Arundel1480–1518
4. Codex Forster, I2 (fols. 41–55)1480–1490
5. MS Bca.1489
6. Codex Trivulzianusca. 1489
7. MS C1490
8. Codex Madrid, II(fols. 141–157)1491–1493
9. MS A1492
10. Codex Madrid, I1492–1497
11. Codex Forster, II1,II2,III1493–1495
12. MS H1493–1494
13. MS Mca. 1495
14. MS I1495–1494
15. MS L1497; 1502–1503
16. Codex Madrid, II (fols. 1–140)1503–1505
17. MS K11504
18. MS K21504–1509
19. Codex Forster, I11505
20. Codex on Flight...1505
21. Codex Leicesterca. 1506
22. MS Dca.1508
23. MS F1508–1509
24. MS K31509–1512
25. Anatomical Folio Aca. 1510
26. MS G1510–1516
27. MS E1513–1514

Note: Not all scholars are in agreement as to the years given above. It is, however, a matter of plus or minus one or two years.

I. Original Works. Published treatises (compilations) are Treatise on Painting (abr.), pub. by Rafaelle du Fresne (Paris, 1651), complete treatise, as found in Codex Urbinas latinus 1270, trans. into English, annotated, and published in facs. by Philip A. McMahon (princeton, 1956); and Il trattato del moto e misura dell acqua..., pub. from Codex Barberinianus by E. Carusi and A. Favoro (Bologna, 1923).

Published MSS are Codex Atlanticus, facs. ed. (Milan, 1872 [inc.], 1894–1904), consisting of 401 fols., each containing one or more MS sheets (Codex is in the Biblioteca Ambrosiana, Milan); MSS A—M and Ashburnharn 2038 and 2037 (in the library of the Institut de France), 6 Vols., Charles Ravaisson-Mollien, ed. (Paris, 1881–1891), consisting of 2,178 facs. reproducing the 14 MSS in the Institut de France and Bibliotheque Nationale, with transcription and French trans.; Codex Trivulzianus, transcription and annotation by Luca Beltrami (Milan, 1891), containing 55 fols.; Codex on the Flight of Birds, 14 fols. by Theodore Sabachnikoff, transcribed by Giovanni Piumati, translated by C. Ravaisson-Mollien (Paris, 1893, 1946); The Drawings of Leonardo da Vinci at Windsor Castle, cataloged by Kenneth Clark, 2nd ed., rev. with the assistance of Carlo Pedretti (London, 1968), containing 234 fols.: repros. of all the drawings at Windsor, including the anatomical drawings (notes are not transcribed or translated where this has been done in other works such as the selections of J. P. Richter, Anatomical Folios A and B, and the Quaderni d’anatomia; see below); Dell’anatomia Fogli A, Pub. by T. Sabachnikoff and G. Piumati (Turin, 1901); Dell’anatomia fogli B, pub. by T. Sabachnikoff and G. Piumati (Turin, 1901); Quaderni d’anatomia, 6 vols., Ove C. L. Vangensten, A. Fonahn, and H. Hopstock, eds. (Christiania, 1911–1916), all the anatomical drawings not included in Folios A and B; Codex Leicester (Milan, 1909), 36 fols., pub. by G. Calvi with the title Libro originale della natura peso e moto Belle acque (Codex is in the Leicester Library, Holkham Hall, Norfolk); Codex Arundel, a bound vol. marked Arundel 263, pub. by the Reale Commissione Vinciana, with transcription (Rome, 1923–1930), containing 283 fols. (Codex is in British Museum); and Codex Forster, 5 vols., 304 fols., pub. with transcription by the Reale Commissione Vinciana (Rome, 1936) (Codex is in the Victoria and Albert Museum, London).

MSS are J. P. Richter, The Literary Works of Leonardo da Vinci, 2 vols. (London, 1970), containing a transcription and English translation of a wide range of Leonardo’s notes used as a reference work in Clark’s Catalogue of the Drawings at Windsor Castle; and E. MacCurdy, The Notebooks of Leonardo do Vinci, 2 vols. (London, 1939; 2nd ed., 1956), the most extensive selection of Leonardo’s notes.

II. Secondary Literature. The following works can be used to obtain a general picture of Leonardo’s scientific work: Mario Baratta, Leonardo do Vinci ed i problenn delta terra (Turin, 1903); Elmer Belt, Leonardo the Anatomist (Lawrence, Kan., 1955); Girolamo Calvi, I manoscritti di Leonardo da Vinci (Rome, 1925); B. Dibner, manoscritti di Vinci, Military Engineer (New York, 1946), and Leonardo da Vinci, Prophet of Automation (New York, 1969); Pierre Duhem, Etudes sur Leonard de Vinci (Paris, 1906–1913; repr. 1955); Sigrid Esche-Branunfels, Leonardo da Vinci, das anatomische Werk (Basel, 1954); Giuseppe Favoro, Leonardo da Vinci, i medici e la medicina (Rome, 1923), and “Leonardo da Vinci e l’anatomia,” in Scientia, no. 6 (1952), 170–175; Bertrand Gille, The Renaissance Engineers (London, 1966); I. B. Hart, The World of Leonardo da Vinci (London, 1961); L. H. Heydenreich, Leonardo da Vinci (Berlin, 1944), also trans. into English (London, 1954); K. D. Keele, Leonardo da Vinci on the Movement of the Heart and Blood (London, 1952); “The Genesis of Mona Lisa,” in Journal of the History of Medicine,14 (1959), 135; and “Leonardo da Vinci’s Physiology of the Senses,” In C. D. O’Malley, ed., Leonardo’s Legacy (BerKeley–Los Angeles, 1969); E. Mac Curdy, The mind of Leonardo da Vinci (New York, 1928); J.P.McMurrich, Leonardo da Vinci, the Anatomist (Baltimore, 1930); Roberto Marcolongo, Studi Vinciani; Memorie Sulla geometrai e la meccanica di Leonardo da Vinci (Naples, 1937); and A. Marinoni, “The Manuscripts of Leonardo da Vinci and Their Editions,” in Leonardo Saggie e ricerche (Rome, 1954).

See also C. D. O’malley, ed., Leonardo’s Legacy—an International Symposium (Berkeley—Los Angeles, 1969); C.D.O’Malley and J. B. de C. M. Saunders, Leonardo da Vinci on the Human Body (New York, 1952); Erwin Panofsky, The Codex Huygens and Leonardo da Vinci’s Art Theory (London 1940); A. Pazzini, ed.,Leonardo da Vinci. II tratto della anatomia (Rome, 1962); Carlo Prdretti, Documenti e memorie riguardanti Leonardo da Vinci a Bologna e in Emilia(Bologna, 1953); Studi vinciani (Geneva, 1957); andLeonardo da Vinci on Painting—a Lost Book (Libro A) (london, 1965); Raccoltavinciana, “Commune di Milano, Castello Sforzesco,” I–XX (Milan, 1905–1964); ladislao Reti, “Learti chimiche di Leonardo da Vinci,” in Chimica e l’industria,34 (1952), 655–721; “Leonardo da Vinci’s Experiments on Combustion,” in Journal of Chemical Education,29 (1952), 590; “The Problem of Prime Movers,” in Leonardo da Vinci, Technologist (New York, 1969); and “The Two Unpublished Manuscripts of Leonoardo da Vinci in Madrid,” ibid., I.A.Richter, Selections From the Notebooks of Leonardo da Vinci (Oxford, 1962); Vasco Ronchi, “Leonardo e L’ottica,” in Leonardo saggi e richeche (Rome, 1954); George Sarton, Leonardo de Vinci, ingenieur et savant, Colloques internationaux (Paris, 1953), pp. 11–22; E.Solmi, Scritti vinciani, papers collected by Arrigo Solmi (Florence, 1924); K.T. Steintz, Leonardo da Vinci’s Tratto della pittura (Copenhagen, 1958); Giorgio Vasari,Lives of the Painters and Architects (London, 1927); and V.P.Zubov, Leonardo da Vinci, trans from the Russian by David H. Kraus (Cambridge, Mass, 1968).

The remainder of the bibliography is divided into sections corresponding to those in the text: Technology, Mechanics, Mathematics, and Geology.

Technology. On Leonardo’s work in technology, the following should be consulted: T. Beck,Beitrage zur Geschichte des Maschinenbaues, 2nd ed. (Berlin, 1900), completed in Zeitschrift des Vereines deutscher Ingenieure (1906), 524–531, 562–569, 645–651,777–784; I. Calvi, L’architettura militare di Leonardo da Vinci (Milan, 1943); G. Canestrini, Leonardo costruttore di machine e veicoli (Milan, 1939); B. Dibner, Leonardo da Vinci, Military Engineer (New York, 1946); F.M. Feldhaus, Leonardo der Techniker und Erfinder (Jena, 1922); R. Giacomelli, Gli scritti di Leonardo da Vinci sul volo (Rome, 1936); C. H. Gibbs Smith, “The Flying Machine of Leonardo da Vinci,” in shell Aviation News, no. 194 (1954); The Aeroplane (London, 1960); and Leonardo da Vinci’s Aeronautics (London, 1967); B. Gille , Engineers of the Renaissance (Cambridge, Mass., 1966); I. B. Hart, The Mechanical Investigations of Leonardo da Vinci (London, 1925; 2nd ed., with a foreword by E. A. Moody, Berkeley—Los Angeles, 1963), and The World of Leonardo da Vinci(London, 1961); Leonard de Vinci et L’experience sceintifique au XVI Seicle (Paris, 1952), a collection of articles originally pub. in 1939; R. Marcolongo, Leonardo da Vinci artisa—scienziatoc(Milan, 1939); W.B. Parsons, Engineers and Engineering in the Renaissance (Baltimore, 1939; 2nd ed., Cambridge, Mass., 1968); L. Reti, “Leonardo da Vinci nella storia della macchina a vapore,” in Rivista di ingegneria (1956–1957); L. Reti and B. Dibner, Leonardo da Vinci, Technologist (New York, 1969); G. Strobino, Leonardo da Vinci e la meccanica tessile (Milan, 1953); C. Truesdell, Essays in the History of Mechanics (New York, 1968); L.Tursini, Le armi di Leonardo da Vinci (Milan, 1952); A. Uccelli, Storia della tecnica... (Milan, 1945), and I libri del volvo di Leonardo da Vinci (Milan, 1952); A.P. Usher, A History of Mechanical Inventions, rev.ed. (Cambridge, Mass., 1954); and V.P. Zubov, Leonardo da Vinci (Cambridge, Mass., 1968).

Mechanics Particularly useful as a source collection of pertinent passages on mechanics in the notebooks is A. Uccelli, ed,I libri di meccanica... (Milan, 1942). The Pioneer analytic works were those of P.Duhem, Les origines de la statique, 2 vols. (Paris, 1905–1906), and Etudes sur Leonard de Vinci (Paris, 1906–1913; repr. 1955). These works were the first to put Leonardo’s mechanical works into historical perspective. Their main defect is that a full corpus of Leonardo’s notebooks was not available to Duhem. They are less successful in interpreting Leonardo’s dynamics. Far less perceptive than Duhem’s work is F.Schuster’s treatment of Leonardo’s statics, Zur Mechanik Leonardo da Vincis (Erlangen, 1915), which also suffered because the sources available to him were deficient. A work that ordinarily follows Schuster (and Duhem) is I. B. Hart, The Mechanical Investigations of Leonardo da Vinci(London, 1925; 2nd ed., with foreword by E.A. Moody, Brekeley- Los Angeles, 1963). It tends to treat Leonardo in isolation, although the 2nd ed., makes some effort to rectify this deficiency. The best treatment of Leonaardo’s mechanics remains R. Marcolongo, Studi vinciani: Memorie sulla geomatria e la meccanica di leonardo da Vinci (Naples, 1937). It is wanting only in its treatment of Leonardo’s hydrostatics and the motion of fluids. For a brief but important study of Leonardo’s hydrostatics, see F. Arredi,Le origini dell’idrostatica (Rome, 1943), pp.8–16. For an acute appraisal of Leonardo’s mechanics in general and his fluid mechanics in particular, see C. truesdell,Essays in the History of Mechanics (New York, 1968), pp. 1–83, esp, 62–79. Finally, for the influence of Archimedes on Leonardo, see M. Clkagett, “Leonardo da Vinci and the Medieval Archimedes,” in Physics, 11 (1969), 100–151, esp. 108. 108–113, 119–140.

Mathematics The most thorough study of Leonardo’s mathematical works was carried out in the first part of the twentieth century by R. marcolongo, whose most important writings are: “Le ricerche geometrico—meccaniche di Leonardo da Vinci,” in Atti della Societa italiana delle scienze, detta dei XL, 3rd ser., 23 (1929), 49–100; II trattato di Leonardo da Vinci sulle trasformazioni dei solidi (Naples, 1934); and Leonardo da Vinci artista–scienziato (Milan, 1939). The cited article of C. Caversazzi, “Un’invenzione geometrica di Leonardo da Vinci,” is in Emporium (May 1939), 317–323. Important article sare M. Clagett, “Leonardo da Vinci and the Medieval archimedes,” in Physis, II (1969), 100–151; and C. Pedretti, “The Geometrical Studies,” in K. Clark, The Drawings of Leonardo da Vinci at Windsor Castle, 2nd ed., rev. (London, 1968), I, xlix–liii; and “Leonardo da Vinci: Manuscripts and Drawings of the French Period, 1517–1518,” in Gazette des beauxarts (Nov. 1970), 185–318.

The following studies by A. Marinoni provide a detailed analysis of some of Leonardo’s works: “Le operazioni aritmetiche nei manoscritti vinciani,” in Raccolta vinciana, XIX (Milan, 1962), 1–62; “La teoria dei numeri frazionari nei manoscritti vinciani. Leonardo e Luca Pacioli,” ibid., XX (Milan, 1964), 111–196; and “L’ aritmetica di Leonardo,” in Periodico di matematiche (Dec. 1968), 543–558. See also Marinoni’s L’essere del nulla (Florence, 1970) on the definitions of the “principles” of geometry in Leonardo, and “Leonardo da Vinci,” in Grande antologia filosofica (Milan, 1964), VI, 1149–1212, on the supposed definition of the principle of inertia.

Geolgy. On Leonardo’s work in geology, see the following: Mario Baratta, Leonardo da Vinci ed i Problemi della terra (Turin, 1903); I disegni geografici di Leonardo da Vinci conservati nel Castello di windsor (Rome, 1941); Girolamo Calvi, Introduction, Codex Leicester (Rome, 1909); Giorgio Castelfranco, “Sul pensiero geologico eil paesaggio di Leonardo,” in Achille Marazza, ed., Saggi e Ricerche (Rome, 1954), app. 2; Kenneth Clark, Leonardo da Vinci (Baltimore, 1963) Giuseppe De Lorenzo, Leonardo da Vinci e la geologia (Bologna, 1920); Pierre Duhem, Etudes sur Leonard de Vinci, 3 vols. (Paris, 1906–1913; repr. 1955); Eugene Muentz, Leonardo da Vinci, Artist, Thinker, and Man of Science (New York, 1898); and J. P. Richter, ed.,The Notebooks of Leonardo da Vinci (New York, 1970).

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GEOLOGY. Although often sharing ground and affiliated with other natural sciences, geology at its core is the study of the earth's crust considered with respect to its rock and mineral content, its layered structure, and its dynamic transformations over time. In the United States, the science first emerged as a popular, organized pursuit around 1820, and about half a century later began to look something like the highly technical, professional discipline it is today. The crucial transition in its evolution occurred at the time of the Civil War (1861–1865), which thus serves as a boundary between the two major periods into which the history of American geology may conveniently be divided. In the first—an organizing, professionalizing stage—geologists were primarily engaged in identifying, naming, and classifying rock strata and in gathering information on mineral locations. Geology was greatly appreciated by the public for its educational value, its health benefits (claimed for the exercise and fresh air of field excursions), and its economic utility. It also attracted wide attention because of its unorthodox religious implications. In the second phase, when geology became the preserve of an enlarged corps of trained specialists, it tended to slip from public view even while it was charting paths for western expansion, unearthing the ores and energy resources needed to sustain a burgeoning economy, and performing other useful services. While geology became increasingly technical and inaccessible to the public, the plate tectonics revolution of the 1960s and 1970s made geology momentarily newsworthy, and thereafter there have been signs of the reentry of the science into the public arena as concern over global warming, water shortages, and other environmental problems has grown.

Geology in America Before the Civil War

In the early nineteenth century, geology was a fledgling science. Its practitioners were committed to avoiding the groundless speculations that had marred earlier "theories of the earth" and dedicated themselves to erecting geology on a solid foundation of observational data and well-ascertained facts. At the same time, making a pitch for public support of their endeavors, they gave assurances that geology was exceedingly useful. It could illuminate the earth's structure and chronicle its history, furnish valuable technical advice bearing on the progress of agriculture, mining, and manufacturing, and perhaps even lend confirmation to the biblical accounts of the Creation and the Flood. Receptive to these claims, the American public held geology in high esteem. In fact, during the first half of the nineteenth century it was the most popular of all the sciences. It won a place in the college curriculum, and textbooks setting forth its basic principles appeared. It was the subject of popular works and of primers, of articles in the quarterlies and the newspapers. Geology was a frequent topic for lyceum courses and public lectures, some like the Lowell Lectures in Boston, attracting thousands of auditors. In part, this high level of interest was stimulated by the ethos of "self-improvement" that Americans had adopted. Undergoing rapid growth, geology was making new discoveries in abundance, and it was the part of the educated person to keep abreast of these noteworthy advances in scientific knowledge.

But interest in geology was also stimulated by its bearing on religion. When geologists considered the rates at which geological processes like denudation and sedimentation take place, they were forced to conclude that the earth was millions of years old. How could this finding be reconciled with widely credited inferences from Old Testament history putting the age of the world at 6,000 years? And then there was the newly uncovered fossil record showing that vast stretches of time separated the first appearance on earth of the major types of plants and animals and that most of the ancient forms had become extinct before humans appeared. How could these facts be harmonized with the doctrine of the divine creation of the world in six days set forth in the book of Genesis? Benjamin Silliman Sr. and Edward Hitchcock, among other antebellum geologists, believed in the inspiration and authority of the Bible, but they were also stout champions of geology and did not want to see it succumb to biblical censorship. Certain that Genesis and geology must ultimately agree, they reconciled the two by adopting nonliteral interpretations of Scripture; Silliman, for example, subscribed to the "day-age" view, whereby the days of the Bible were interpreted as geological periods. This kind of harmonizing exegesis had an appeal for a while, but by the middle of the century it had begun to appear less convincing.

Noah's Flood was even easier to reconcile with geology, since it had long been invoked to explain the sculpting the earth's crust had undergone. As suggestive as this idea was, it did not stand up to close scrutiny, and by the mid-1830s the Flood had been abandoned as a universal, geological agency by the leading geologists. Among nonspecialists, of course, these issues were not so quickly resolved, and as long as geology appeared to bear in critical ways on the truth of Scripture, it continued to interest the public.

The perception that geology might be a source of substantial economic benefits also contributed to its popularity. To realize these benefits and join the national campaign for "internal improvements," virtually all the state legislatures authorized geological or natural history surveys. The first of these was instituted in North Carolina in 1823. By 1865, only Oregon and Louisiana had not initiated surveys. From state to state the surveys varied in scope and emphasis, but ordinarily they included a cataloging of the state's mineral deposits, an analysis of its soils for the benefit of farmers, and topographical reconnaissance to determine routes for turnpikes, railroads, and canals. Supported by annual appropriations that the geologists were obliged to justify in their annual reports, surveys would typically last a few years and conclude with the publication of "final reports." Aside from the evidence they presented of the industriousness and scientific acumen of the state geologists and their assistants, these state-funded documents served as valuable publicity for geology and gave evidence of its far-reaching utility. The public was appreciative, although occasionally there were complaints by those who did not want to hear that geological examinations of the state excluded the possibility of finding within its boundaries deposits of desirable mineral substances (coal in New York, for example).

The geologists employed in these surveys were far less specialized and professional than geologists would subsequently become. Among the approximately 500 individuals who published on earth science topics in antebellum America, few cultivated geology exclusively. Typically, their publications extended to other areas of science, notably natural history or chemistry. But whether specialists or not, they had only limited opportunities for making a living in science. Generally it was an avocational pursuit for those who found their principal work in medicine, the church, or business. Nonetheless, a living could be made in geology, and more readily than in most areas of science, since geologists could find employment in government surveys and in private consulting, as well as in college teaching. To be sure, combining the pay from two or more jobs in these different sectors might be necessary to ensure an adequate annual income.

Since as yet there were no graduate programs providing research training (these were inaugurated after the Civil War), there was no standard educational stepladder giving entry to a geological career. Apprenticing and on the-job training as assistants in government surveys gave the best preparation. Providing not only an introduction to the practicalities of fieldwork that were essential to geology, survey work also made available through the many reports it generated a publication outlet for the aspiring geologist. The experience of the state surveys was also important in developing a collective esprit de corps among geologists and spurring them to organize on a national level. The year 1840 saw the founding of the Association of American Geologists, which shortly was to become the Association of American Geologists and Naturalists, and then in 1848 the American Association for the Advancement of Science. These developments bear witness to the fact that the professionalization and institutionalization of science in America was spearheaded by geologists.

As the Civil War approached, American geologists could feel they were part of a flourishing enterprise. The esteem in which geology was held by the public, the career opportunities it afforded, and the still-limited professionalism it practiced were all on the rise. There was pride in the surveying and mapping that had been accomplished in the preceding fifty years and a zest for continuing the exploration of the trans-Mississippi West. Geology was one facet of culture in which Americans no longer needed to feel they were inferior to Europeans. Textbooks now illustrated geological principles with American material, and one fundamental concept adopted by geologists everywhere, that of the geosyncline (a trough-like downwarp of the earth's crust supposed to be foundational in mountain building), had its origins in America.

Geology in America Since the Civil War

Although during the war years geological activity ground nearly to a halt, the end of the conflict launched a new and vibrant era in the cultivation of the earth sciences. Compared with its antebellum history, geology was now much more national in framework and in closer partner-ship with the federal government. The most expensive and highly publicized of the new projects were the federal surveys of the West. Unlike the U. S. government surveys undertaken before the Civil War, they were not primarily military in purpose nor under army direction. They were multifaceted exploring enterprises conducted by such ambitious civilian "entrepreneurs" as F. V. Hayden, Clarence King, and John Wesley Powell. The cost, competitiveness, and overlap of these surveys led in 1879 to their replacement by a consolidated bureau under the Department of the Interior, the United States Geological Survey (USGS). Initially, the USGS was especially concerned with serving the western mining industry, but subsequently its purposes broadened to include mapping the country, studying water resources, researching marine geology, and much else. In the world wars of the twentieth century it gave priority to the provision of strategic materials.

The creation of a consolidated, national framework for geological research was paralleled by the establishment in 1888 of a new association of national scope (or supranational, as it took in all of North America) dedicated to the professional growth of earth scientists. Still active in the twenty-first century and boasting a global membership in excess of 16,000, the Geological Society of America (GSA) holds an annual meeting and sponsors six regional sections that conduct their own yearly meetings. It further serves its members by publishing research papers and monographs, distributing research grants, recognizing outstanding achievements with medals and other honorific awards, and operating an employment clearinghouse. Twenty percent of GSA's members are students, and a wider participation of women in geology is encouraged by the activities of an associated society, the Association for Women Geoscientists. In seeking to achieve its aim of advancing the geosciences, the GSA, shaped by the modern culture of professionalism, has concentrated heavily on the practitioners, on the geoscientists themselves, their recruitment, development, and rewards.

This inner-directed orientation of geology's leaders, in combination with the growing technicality and inaccessibility of the science to outsiders, has opened up a gap between geology and the public that did not exist in the antebellum period. Few people are now drawn to geology because of cosmic or religious implications it is supposed to have. Nor does probing the relations between Genesis and geology currently have any cultural urgency. The GSA, to be sure, has issued a position paper (pro) on the theory of evolution, and more generally it has characterized the organization's vision as "applying geoscience knowledge and insight to human needs and aspirations and stewardship of the Earth." But getting this idealistic message to be taken seriously by an indifferent public has been difficult.

There have been signs that public awareness of geology may once again be stirring. The theory of plate tectonics established in the 1960s and 1970s has been so revolutionary and consequential that some word of it has reached almost everyone. It was a legacy of nineteenth-century geological thinking that throughout the history of the earth, continents and ocean basins have been permanently fixed (save for occasional motions upward or downward). When, starting in 1912, the German meteorologist Alfred Wegener challenged this fixist theory, arguing that continents have drifted laterally, collided, and separated, he made hardly any converts. By the late 1960s, however, continental drift had been incorporated into a new, synthetic theory that supposed the earth's crust to consist of a dozen or so rigid plates that move horizontally and interact with one another in response to heat convection patterns in the mantle. Turning back all challenges, the theory has revolutionized geology, giving it a remarkable unity and coherence and raising its explanatory power many times.

Just as the plate tectonics revolution was occurring, James Lovelock was publicizing his Gaia Hypothesis (in its biosphere the Earth functions as a single, self-regulating superorganism), the science of ecology was gaining broad recognition, and environmental alarms were registering in the public consciousness. One upshot of these developments has been a new and earnest regard for the planet, incorporating the knowledge and perspective of many fields—geology, biology, oceanography, atmospheric sciences, climatology, and so forth. If the idea is to understand how we depend on the environment and how we can keep it in balance, then help from all these sciences and others may be required. The processes to be understood are complex. They function as "systems" that only a multidisciplinary approach can unravel. Enough is at stake to suggest that geology, which is already a multi-disciplinary field, will once again gain public attention.


Aldrich, Michele L. New York Natural History Survey, 1836– 1845: A Chapter in the History of American Science. Ithaca, N. Y. : Paleontological Research Institution, 2000.

Goetzmann, William H. Exploration and Empire: the Explorer and the Scientist in the Winning of the American West. New York: Knopf, 1966.

Kohlstedt, Sally Gregory. "The Geologists' Model for National Science. 1840–1847," Proceedings of the American Philosophical Society, 1974, 118: 179–195.

Manning, Thomas G. Government in Science: The U. S. Geological Survey, 1867–1894. Lexington: University of Kentucky Press, 1967.

Merrill, George P. The First One Hundred Years of American Geology. New Haven, Conn. : Yale University Press, 1924.

Newell, Julie Renee, "American Geologists and Their Geology: The Formation of the American Geological Community, 1780–1865," Ph. D. Diss., Univ. of Wisconsin-Madison, 1993.

Oreskes, Naomi. The Rejection of Continental Drift: Theory and Method in American Earth Science. New York and Oxford: Oxford University Press, 1999.

Schneer, Cecil J., ed. Two Hundred Years of Geology in America: Proceedings of the New Hampshire Bicentennial Conference on the History of Geology. Hanover, N. H. : University of New Hampshire, 1979.

Robert H.Silliman

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GEOLOGY. Geology was only in the process of becoming a recognized science near the close of the eighteenth century. Tracing geology's root sources, during the several centuries prior to its emergence as a distinct science, requires attention to varied forms of activity and knowledge, including (1) practical activities such as quarrying, mining, surveying, and the metallurgical arts; (2) descriptive and classificatory inquiries in fields of natural history such as mineralogy and physical geography; (3) philosophical explorations of the causes of the formation of minerals, stones, and crystals; (4) history proper, which is to say chronological and antiquarian research; and (5) efforts to construct a theory of the earth, a genre that began to flourish especially after the middle of the seventeenth century.


Growing confidence in the practical value of systematic knowledge lay behind efforts to survey mineral resources and promote their exploitation. The writings of the German mining physician Georgius Agricola (14941555) are representative of increasingly acute descriptions and rationalizations of technical procedures for extracting and treating those resources. By the seventeenth century, under state ownership or patronage of mining authorities in several Continental countries, formalized institutes were being founded as centers for instruction and analysis in the extraction industries. The leading eighteenth-century example was the Saxon Bergakademie (Mining Academy) at Freiberg, where Abraham Gottlob Werner (17491817) achieved fame as both teacher and theoretician. Similar practical and economic motives lay behind royal support for a French mineralogical survey launched in the 1760s.

Until well into the eighteenth century, the term fossil referred comprehensively to things found in or dug out of the ground. Renaissance naturalists such as the Swiss physician Conrad Gessner (15161565) undertook to codify knowledge of fossils, through both observation of specimens and study of texts from Greco-Roman antiquity. Such efforts at literary compilation were echoed by the enthusiasm of collectors (such as the Dane Ole Worm [15881654] and the Jesuit polymath Athanasius Kircher [1601?1680]) for assembling displays of stones, gems, and other "natural antiquities." How stones form, and the possible causative roles played by water or generative seeds in that process, was a central question of early modern natural philosophy. It was perhaps most prominently posed in chemical cosmogonies from Jean Baptiste van Helmont (15791644) to Georg Ernst Stahl (16601734), and physicians regularly addressed it when explaining the formation of bladder stones. Of obvious relevance was assaying of mineral waters, one of the most frequently treated topics of geological investigation during the sixteenth and seventeenth centuries.

Related to these problems was the prolonged debate concerning the origins of "figured stones," or fossil bodies of regular form. One group of theories attributed these bodies to generative powers or seeds indigenous to the earththe mineral domain being considered capable of engendering "intrinsic fossils" through its own specific powers, analogous to those of plants or animals. Such theories were effectively modified toward the end of the seventeenth century, particularly by the Danish anatomist Niels Stensen (Nicolaus Steno, 16381686) and some contemporaries. While employed at the Tuscan court, Steno recognized that the fossils known as glossopetrae resembled sharks' teeth. In his examination of "solid bodies contained naturally within solids," Steno developed a lucid analysis of the processes of sedimentation and petrifaction whereby an actual tooth or other durable organic part might become preserved within solid rock, thus making it an "extrinsic" fossil object. Extrinsic fossils were treated by many naturalists as relics of the biblical Flood, but such "diluvial" interpretations came under broad attack during the eighteenth century as difficulties multiplied for those viewing fossils as remnants of a single event within the time constraints of orthodox biblical chronology.

Advances in antiquarian scholarship during the seventeenth century, meanwhile, provided new standards for authenticating, dating, and interpreting historical relics and records, whether sacred, civil, or natural (terms such as monument or inscription were commonly applied to both human and natural productions). Thus, increasingly rigorous and critical analytical procedures used to study the human pastoften with the aim of confirming historical knowledge found in the Biblewere applied simultaneously to comprehension of the earth's history, extending backward in time from the reconstructed physical geography of the classical era. Finally, as European scholars took Chinese historical records and New World inhabitants into consideration, comparisons of biblical chronology with archaeological and historical discoveries about non-Western peoples yielded doubts about the sufficiency of classical texts, including the Bible, as sources of historical information applicable to all of humanity. Such developments promoted lines of investigation that eventually led to a separation of natural history from civil history, and conviction grew that nature has had a long prehuman history.

Notwithstanding various challenges posed by geological activities and thinking to traditional religious doctrines, pursuit of geological questions up through 1800 proceeded with wide acceptanceoften with hearty endorsementof the presumed consistency of natural knowledge with revealed knowledge. It remained unusual for geological writers to dispute the compatibility of their scientific endeavor with religiously sanctioned belief in the divine superintendence of nature; few geological authors distanced themselves very far from a vision of nature laden with moral meaning.


While much early modern study of minerals and fossils consisted of examining specimens in the cabinet or museum, an ethos grew emphasizing travel and field observation, especially during the eighteenth century. Notable among the results were sustained efforts to discern the configurations of mountains and the patterns of distribution in their constituent rock masses. Around 1750 a consensus began to develop, distinguishing relatively unstructured and nonfossiliferous "primary" rocks, often found in the core districts of mountain ranges, from the stratified and frequently fossiliferous "secondary" rocks. Whether systematic distinctions between these types of rocks might promise access to a satisfactorily inclusive account of the earth's history since its inception was contested; some thought the evidence indicated a series of changes ("revolutions") of perhaps indeterminate number and scope. In general, a broadly shared sense of satisfaction with real progress in precise description of geological phenomena was not matched with agreement about which phenomena mattered most, or about their proper causal explanation. A strong preference existed for explaining the origins and transformations of most geological features through the agency of water ("Neptunism"), although field investigations were gradually yielding information warranting expanded roles for "fire" or heat. Aqueous agency tended to be seen as ordered and constructive (the organized strata of the earth's crust were, after all, mainly sedimentary), whereas fire was commonly viewed as a cause of disorder and disfigurement. The eighteenth century also witnessed a widening adoption of interpretive attitudes that have in retrospect been called "actualistic": this entailed the presumption that causal explanations should rely only on natural agents of types empirically known to operate. ("Actualism" thus differed from nineteenth-century uniformitarianism, which in addition to presuming continuity of kinds or types of cause also assumed continuity in the rate or intensity of their operation.)

Notwithstanding nineteenth-century attacks on the intellectual consequences of theories of the earthCharles Lyell argued in Principles of Geology (vol. 1, 1830) that they promoted intellectual indolencein their post-Cartesian heyday such syntheses or systems tended to serve geological investigation as both motivators for and receptacles of new information and drew attention to geological problems. Whether comprehensive theories constituted good science became increasingly controversial in the second half of the eighteenth century, especially in debates over the merits of theories published by Georges Louis Leclerc Buffon (17071788). Late Enlightenment skepticism about geological "systems" helps explain the generally inhospitable reception given the Theory of the Earth (1788, 1795) offered by the deistic Scottish philosopher James Hutton (17261797). His was a synthetic perspective on the maintenance of geological conditions propitious for support of life on the earth's surface, through a dynamic equilibrium between internal processes of heat-driven rock consolidation and elevation on one hand and external processes of erosion and deposition on the other (the original expression of what has since come to be known as the geostrophic cycle).

In the last quarter of the eighteenth century the science of geognosy (German Geognosie ) made a bid for recognition as the leading means of analyzing mineral phenomena on a local and by extension even a global scale. Geognosy was a method or doctrine taught by Werner, at Freiberg, to an international cadre of students, most of whom were preparing for careers in their respective mining establishments. It elaborated on the litho-stratigraphic insights traceable back to Steno (since adapted and extended by other naturalists), and on skills in mineral identification, to develop recognition of how distinct rock masses relate to one another in subterranean space. Wernerian geognosy produced a key new geological concept, the "formation," defined essentially as a rock mass distinguishable in its lithological character and evident mode of origin, and thus as presumably formed at a given point in time. The formation, as a time-specific rock entity, became the focus of research on the relative positions of differentiated geological elements in the earth's crust (stratigraphy), and thus on their relative ages.

Geology'semergenceasadistinctsciencearound 1800 marked a momentous transformation in the history of Western science: an unprecedentedly definitive investment in nature with a sense of historical development. The classic aim of natural philosophy, prior to this shift of conception, had been confined mainly to the delineation of a presumably fixed order of nature, acting through processes usually believed not to have generated substantially altered configurations in the natural framework or in the objects furnishing it. With the advent of historical geology, the sciences added to their agenda the objective of tracing nature's successive changes. A portentous outcome of this new kind of research was the dawning cognizance, at the end of the eighteenth century, of the reality of biological extinction.


The complications of disciplinary history apply with special force to geology in the early modern period; during most of this time no geological discipline existed. At least until recently, histories of geology have most often been written as retrospective accounts of the science's ancestry. Leading historical interpretations, founded by nineteenth- and twentieth-century geologists wishing to understand how their science came to take its modern form (or to use history as a tool to advance their particular conception of the science), tended to yield Whiggish historical accounts assigning credit or blame in accord with the degree to which various figures or scientific approaches contributed to, or obstructed, geology's progress. This kind of history thus tended also to obscure the motivations and intentions of many of the relevant actors, since few of them (at least until the late eighteenth century) conceived of the establishment of geology as their purpose. Genuinely historical recovery of geology's antecedents requires consultation of research literatures addressing the diverse fields in which, looking back, geological topics are seen to have been treated. Some of the better modern historical researchcarried out largely within the "retrospective" tradition, but in calculated avoidance of Whig historyhas called into question a long-standing Anglophone tendency to honor British over Continental strands in early geology's development, and to redress heavy emphasis on the physical and historical features of certain theories of the earth as preludes to geology, in favor of greater roles for descriptive and chemical-mineralogical enterprises (cf. Laudan). Modern scholarship has also tended to draw back from an earlier inclination to identify a single founder or "father" of geologyHutton was long a British favorite, Werner a Continental oneand to see in geology, instead, a creature of multiple parentage.

See also Buffon, Georges Louis Leclerc ; Earth, Theories of the ; Gessner, Conrad ; Scientific Method ; Steno, Nicolaus .


Ellenberger, François. Histoire de la géologie. 2 vols. Paris, 19881994.

Gohau, Gabriel. Les sciences de la terre aux XVIIe et XVIIIe siècles: Naissance de la géologie. Paris, 1990.

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Kenneth L. Taylor, Kerry V. Magruder

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179. Geology

See also 133. EARTH ; 283. MOUNTAINS ; 385. STONES ; 411. VOLCANOES .

the use of aerial observation and photography in the study of geological features. aerogeologist, n. aerogeologic, aerogeological, adj.
the branch of geology concerned with the adaptability of land to agriculture, soil quality, etc.
metamorphism from simple to more complex minerals, usually occurring deep beneath the earths surface. See also katamorphism , metamorphism . anamorphic, anamorphotic, adj.
a minuteness of rock texture so fine that individual grains are invisible to the naked eye. aphanite, n.
archeogeology, archaeogeology
the branch of geology that studies the geological formations of the remote past. archeogeologic, archaeogeologic, archeogeological, archaeogeological, adj.
the formation of breccia, or masses of rock composed of fragments of older rock fused together.
brontolith, brontolite
a thunderstone or meteoric rock.
the theory that geological changes have been caused by sudden upheaval rather than by gradual and continuing processes. Cf. uniformitarianism. catastrophist, n.
the measurement of the elevations and slopes of mineral strata or of cuttings into rock formations. clinometer, n. clinometric, clinometrical, adj.
a small mass of rock composed of the petrified fecal remains of animals.
the study of surface of the earth or the moon.
the process of movement that causes the earths crust to form continents, mountains, etc. diastrophic, adj.
a geological theory that maintains that some geological phenomena can be explained by extensive flooding of large areas of the earths surface or by an equally strong condition of the weather.
epeirogeny, epeirogenesis
the vertical movement or tilting of the earths crust, affecting broad expanses of continents. epeirogenic, epeirogenetic, adj.
the process of metamorphism. See also 44. BIOLOGY ; 122. DISEASE and ILLNESS . epigenetic, adj.
one who considers geological phenomena to be the result of the action of streams.
a branch of geology that studies the constituent parts of the earth, its atmosphere and water, its crust, and its interior condition. geognosist, geognost, n. geognostic, adj.
the branch of geology that studies the structure of the earths crust; structural geology. Also called geotectonics. geotectonic, adj.
the branch of geology that measures temperatures deep below the surface of the earth; geologic thermometry.
the branch of geology that studies the nature, distribution, and movement of glaciers and their effects upon the earths topography. glaciologist, n. glaciological, adj.
homotaxis, homotaxy
the condition of being arranged in the same way, especially stratified layers that are similar in arrangement and place but not contemporaneous. homotaxic, adj.
the study of water both on and beneath the earths surface. hydrogeological, adj.
the general equality of pressure in the crust of the earth. isostatic, adj.
metamorphism from complex to simpler minerals, usually occurring at or near the earths surface. See also anamorphism, metamorphism. katamorphic, adj.
a small stone ejected by a volcano.
the branch of geology that studies ponds and lakes. limnologist, n.
the process by which loose mineral fragments or particles of sand are solidifled into stone.
the science of explaining the minerals of which the earth is composed, their origins, and the cause of their form and arrangement.
Rare. the study of rocks.
the branch of geology that studies the mineral composition and structure of rocks, usu. macroscopically. Cf. petrography. lithologic, lithological, adj.
a rock or stone formed by natural processes in such a way that it appears to have been artificially fashioned.
1 . the process of change in the form and structure of rocks by the agency of heat, water, and pressure.
2 . the change of particular types of rock, as limestone into marble. Also called epigenesis. See also 74. CHANGE . metamorphic, adj.
the process of chemical change in rocks or other mineral masses that results in the formation of new rocks or minerals. Also metasomatosis.
1 . a very small isotropic needlelike crystal, found usually in volcanic rocks.
2 . a very small stone tooi or part of a tool, as a tooth of a primitive saw. microlithic, adj.
the branch of geology that studies the physical and chemical structures of minerals. mineralogist, n. mineralogic, mineralogical, adj.
the now obsolete theory that all rock surfaces were formed by the agency of water. Cf. plutonism . neptunist, n.
the process by which mountains are created. orogenic, orogenetic, adj.
mineralogy. Also called oryctognosy.
paleopedology, palaeopaedology
a branch of soil science that studies the soils of past geologie times. paleopedologist, palaeopaedologist, n. paleopedologic, palaeopaedologic, paleopedological, palaeopaedological, adj.
a phenomenon in which one mineral encloses another. perimorphic, perimorphous, adj.
petrogensis, petrogeny
the branch of petrology that studies the formation of rocks.
the branch of geology that describes and classifies rocks, usually after microscopic study. Cf. lithology . petrographer, n. petrographic, petrographical, adj.
the branch of geology that studies the origin, structure, composition, changing, and classification of rocks. petrologist, n. petrologic, petrological , adj.
the theory that all rock surfaces have solidified from magmas, some at great depths below the surface of the earth. Cf. neptunism. plutonist, n.
the process by which ores and minerals are formed from the action of vapors produced by igneous magmas. pneumatolytic, adj.
the study of iron or copper sulfides, called pyrites.
the layer of disintegrated and decomposed rock fragments, including soil, lying above the solid rock of the earths crust. Also called mantle rock.
the branch of geology that studies the classification, correlation, and interpretation of stratified rocks. stratigrapher, n. stratigraphic, stratigraphical, adj.
the study of the structure and behavior of the earths crust. tectonic , adj.
the thesis that early geological processes were not unlike those observed today, i.e., gradually occurring. Cf. catastrophism. uniformitarian, n.
a fragment of rock embedded in another kind of rock.

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geology, science of the earth's history, composition, and structure, and the associated processes. It draws upon chemistry, biology, physics, astronomy, and mathematics (notably statistics) for support of its formulations.

Branches of Geology

Geology is divided into several fields, which can be grouped under the major headings of physical and historical geology.

Physical Geology

Physical geology includes mineralogy, the study of the chemical composition and structure of minerals; petrology, the study of the composition and origin of rocks; geomorphology, the study of the origin of landforms and their modification by dynamic processes; geochemistry, the study of the chemical composition of earth materials and the chemical changes that occur within the earth and on its surface; geophysics, the study of the behavior of rock materials in response to stresses and according to the principles of physics; sedimentology, the science of the erosion and deposition of rock particles by wind, water, or ice; structural geology, the study of the forces that deform the earth's rocks and the description and mapping of deformed rock bodies; economic geology, the study of the exploration and recovery of natural resources, such as ores and petroleum; and engineering geology, the study of the interactions of the earth's crust with human-made structures such as tunnels, mines, dams, bridges, and building foundations.

Historical Geology

Historical geology deals with the historical development of the earth from the study of its rocks. They are analyzed to determine their structure, composition, and interrelationships and are examined for remains of past life. Historical geology includes paleontology, the systematic study of past life forms; stratigraphy, of layered rocks and their interrelationships; paleogeography, of the locations of ancient land masses and their boundaries; and geologic mapping, the superimposing of geologic information upon existing topographic maps.

Historical geologists divide all time since the formation of the earliest known rocks (c.4 billion years ago) into four major divisions—Precambrian time and the Paleozoic, Mesozoic, and Cenozoic eras. Each, except the Cenozoic, ended with profound changes in the disposition of the earth's continents and mountains and was characterized by the emergence of new forms of life (see geologic timescale). Broad cyclical patterns, which run through all historical geology, include a period of mountain and continent building followed by one of erosion and, in turn, by a new period of elevation.

Evolution of Geology

Early Geologic Studies

Observations on earth structure and processes were made by a number of the ancients, including Herodotus, Aristotle, Lucretius, Strabo, and Seneca. Their individual efforts in the natural history of the earth, however, provided no sustained progress. Their major contribution is that they attributed the phenomena they observed to natural and not supernatural causes. Many of the ideas expressed by these men were not to resurface until the Renaissance. Later Leonardo da Vinci correctly speculated on the nature of fossils as remains of ancient organisms and on the role that rivers play in the erosion of land. Agricola made a systematic study of ore deposits in the early 16th cent. Robert Hooke and Nicolaus Steno both made penetrating observations on the nature of fossils and sediments.

Evolution of Modern Geology

Modern geology began in the 18th cent. when field studies by the French mineralogist J. E. Guettard and others proved more fruitful than speculation. The German geologist Abraham Gottlob Werner, in spite of the many errors of his specific doctrines and the diversion of much of his energy into a fruitless controversy (in which he maintained that the origin of all rocks was aqueous), performed a great service for the science by demonstrating the chronological succession of rocks.

In 1795 the Scottish geologist James Hutton laid the theoretical foundation for much of the modern science with his doctrine of uniformitarianism, first popularized by the British geologist John Playfair. Largely through the work of Sir Charles Lyell, this doctrine replaced the opposing one of catastrophism. Geology in the 19th cent. was influenced also by the work of Charles Darwin and enriched by the researches of the Swiss-American Louis Agassiz.

In the 20th cent. geology has advanced at an ever-increasing pace. The unraveling of the mystery of atomic structure and the discovery of radioactivity allowed profound advances in many phases of geologic research. Important discoveries were made during the International Geophysical Year (1957–58), when scientists from 67 nations joined forces in investigating problems in all branches of geology. The systematic survey of the floors of the earth's oceans brought radical changes in concepts of crustal evolution (see seafloor spreading; plate tectonics).

As a result of numerous flyby spacecraft, geological studies have been extended to include remote sensing of other planets and satellites in the solar system and the moon. Laboratory analysis of rock samples brought back from the moon have provided insight into the early history of near-earth space. On-site analyses of Martian soil samples and photographic mapping of its surface have given clues about its composition and geologic history, including the possibility that Mars once had enough water to form oceans. Photographs of the many active volcanoes on Jupiter's moon Io have provided clues about earth's early volcanic activity. Geological studies also have been furthered by orbiting laboratories, such as the six launched between 1964 and 1969 in the Orbiting Geophysical Observatory (OGO) series and the Polar Orbiting Geomagnetic Survey (POGS) satellite launched in 1990; remote-imaging spacecraft, such as the U.S. Landsat program (Landsat 8, launched in 2013, is the most recent) and French SPOT series (SPOT 6, launched in 2012, is the most recent in the program); and geological studies on space shuttle missions.


See N. Coch and A. Ludman, Physical Geology (3d ed. 1991); L. S. Fichter et al., Earth Materials and Earth Processes (3d ed. 1991); L. Margulis and L. Olendenski, Environmental Evolution: Effects of the Origin and Evolution of Life on Planet Earth (1992); R. H. Dott, Jr., and D. R. Prothero, Evolution of the Earth (5th ed. 1994); E. A. Keller, Environmental Geology (7th ed. 1996); S. Chernicoff and C. Fox, Essentials of Geology (1998); E. J. Tarbuck and F. K. Lutgens, The Earth: An Introduction to Physical Geology (6th ed. 1998).

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Geology, the study of planetary processes and histories, has applications in forensic science that date back to the 19th century fictional detective Sherlock Holmes. The principles and techniques of geology are most commonly used to identify the sources, or provenance, of rock or soil particles associated with a crime. Other applications include the use of principles borrowed from stratigraphy (the study of sequences of rocks) and structural geology (the study of deformed rocks) to infer a series of events that may be important in civil and criminal cases. Experts in the geology of specific regions can also help to identify locations using their knowledge of rock types and landforms.

Sherlock Holmes, the fictional detective created by the British author Arthur Conan Doyle (18591930), was able to distinguish different types of soils and use this information to infer the places to which suspects had traveled. The first known non-fictional use of geological techniques in a criminal investigation, however, did not occur until 1904. In that year, German chemist Georg Popp helped to identify a murder suspect by matching coal dust and particles of the mineral hornblende found on a handkerchief to the same substances at a coal processing plant and quarry that employed the suspect. Several years later, Popp matched layers of goose droppings, distinctive red sandstone fragments, and a mixture of coal, brick, and cement dust to materials at a murder victim's home, the place where the body was found, and the place where the murder weapon was found. Just as importantly, Popp determined that the suspect's shoes contained no distinctive quartz particles from field where the suspect claimed to be walking at the time of the murder. Popp's work, like the work of modern day forensic geologists, made use of the geologic concept of provenance, which is a description of the origin and history of a soil or rock particle, to place suspects in specific locations and disprove an alibi. His use of the sequence of layered goose droppings, sandstone fragments, and dust to infer the sequence in which the suspect visited those locations was an application of the principles of stratigraphy.

Geologists can often determine the geographic source and history, or provenance, of sand grains or soil particles found at a crime scene, especially if distinctive minerals or microfossils are found. This usually involves microscopic examination of soil or rock samples using magnifying glasses, reflected light microscopes , polarized transmitted light microscopes, and, in some cases, sophisticated instruments such as electron microscopes or microprobes. Even if details are not visible to the naked eye, microscopic examination can show that two seemingly similar samples of sand are composed of particles with different chemical composition, size, or shape. In some cases, the geologic details may be specific enough to place a suspect at a certain outcrop or in a specific watershed. This kind of information can be presented as evidence by geologists acting as expert witnesses in civil and criminal cases.

One of the most widely known uses of sand provenance studies in a forensic investigation involves balloons carrying explosive and incendiary bombs over the United States during World War II. Meteorological information was used to determine that the balloons were being launched in Japan and carried across the Pacific Ocean by the jet stream. The balloons carried sand-filled bags as ballast, some of which were automatically released to maintain altitude as temperature dropped each night, and the U.S. Geological Survey was asked to identify the source of the ballast sand found at balloon crash sites. The sand contained an unusual mixture of mineral grains, diatoms, and foraminifera (single celled organisms that secrete siliceous and calcareous shells), and mollusk shell pieces but no coral fragments. Government geologists studied maps and reports published before the war, and determined that sand with that unique composition existed at only two places along the Japanese coast. Those locations turned out to be very close to the actual launching points. Identification of sand grains and soil particles has been an important part of high-profile criminal cases such as the 1978 kidnapping and murder of Italian prime minister Aldo Moro and the unsuccessful attempt by Mexican federal police to cover up the 1985 kidnapping, torture, and murder of U.S. Drug Enforcement Agency operative Enrique Camarena Salazar and his pilot Alfredo Zavala Avelar.

Geologic details in images can also help investigators determine the locations in which photographs or video recordings were made. In the days after the September 11, 2001, terrorist attacks on New York City and Washington, D.C., for example, American geologists who had worked in Afghanistan were able to identify rock outcrops shown in video tapes of the terrorist leader Osama bin Laden, placing him in a certain part of that country. This use of geologic information was widely publicized and subsequent tapes were made against a cloth background in order to make identification more difficult.

see also Forensic science; Geospatial imagery; GIS; Meteorology; Minerals; Physical evidence.

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Geology is the study of the earth. Specifically, geologists may study mountains, valleys, plains, sea floors, minerals , rocks, fossils , and the processes that create and destroy each of these. Geology consists of two broad categories of study. Physical geology studies Earth's materials (erosion , volcanism, sediment deposition, etc.) that create and destroy the materials and landforms . Historical geology explores the development of life by studying fossils (petrified remains of ancient life) and the changes in land (for example, distribution and latitude ) via rocks. The two categories overlap in their coverage: for example, to examine a fossil without also examining the rock that surrounds it tells only part of the preserved organism's history.

Physical geology further divides into more specific branches, each of which deals with its own part of Earth's materials, landforms, and/or processes. Mineralogy and petrology investigate the composition and origin of minerals and rocks, respectively. Sedimentologists look at sedimentary rocks , products of the accumulation of rock fragments and other loose Earth materials, to determine how and where they formed. Volcanologists tread on live, dormant, and extinct volcanoes checking lava , rocks and gases. Seismologists set up instruments to monitor and to predict earthquakes and volcanic eruptions . Structural geologists study the ways rock layers bend and break. Plate tectonics unifies most aspects of physical geology by demonstrating how and why plates (sections of Earth's outer crust ) collide and separate and how that movement influences the entire spectrum of geologic events and products.

Fossils are used in historical geology as evidence of the evolution of life on Earth. Plate tectonics adds to the story with details of the changing configuration of the continents and oceans . For years paleontologists observed that the older the rock layer, the more primitive the fossil organisms found therein, and from those observations developed evolutionary theory. Fossils not only relate evolution, but also speak of the environment in which the organism lived. Corals in rocks at the top of the Grand Canyon in Arizona, for example, show a shallow sea flooded the area around 290 million years ago. In addition, by determining the ages and types of rocks around the world, geologists piece together continental and oceanic history over the past few billions of years. For example, by matching fossil and tectonic evidence, geologists reconstructed the history and shape of the 200300 million year-old supercontinent, Pangaea.

Many other sciences also contribute to geology. The study of the chemistry of rocks, minerals, and volcanic gases is known as geochemistry . The physics of the earth is known as geophysics. Paleobotanists study fossil plants. Paleozoologists reconstruct fossil animals. Paleoclimatologists reconstruct ancient climates.

Much of current geological research focuses on resource utilization. Environmental geologists attempt to minimize human impact on Earth's resources and the impact of natural disasters on human kind. Hydrology and hydrogeology , two subdisciplines of environmental geology, deal specifically with water resources. Hydrologists study surface water whereas hydrogeologists study ground water. Both disciplines try to minimize the impact of pollution on these resources. Economic geologists focus on finding the minerals and fossil fuels (oil, natural gas , coal ) needed to maintain or improve global standards of living. Extraterrestrial geology, a study in its infancy, involves surveying the materials and processes of other planets, trying to unlock the secrets of the universe and even to locate mineral deposits useful to those on Earth.

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Geology is the scientific study of Earth. Geologists study the planetits formation, its internal structure, its materials, its chemical and physical processes, and its history. Mountains, valleys, plains, sea floors, minerals, rocks, fossils, and the processes that create and destroy each of these are all the domain of the geologist. Geology is divided into two broad categories of study: physical geology and historical geology.

Physical geology is concerned with the processes occurring on or below the surface of Earth and the materials on which they operate. These processes include volcanic eruptions, landslides, earthquakes, and floods. Materials include rocks, air, seawater, soils, and sediment. Physical geology further divides into more specific branches, each of which deals with its own part of Earth's materials, landforms, and processes. Mineralogy and petrology investigate the composition and origin of minerals and rocks. Volcanologists check lava, rocks, and gases on live, dormant, and extinct volcanoes. Seismologists set up instruments to monitor and predict earthquakes and volcanic eruptions.

Historical geology is concerned with the chronology of events, both physical and biological, that have taken place in Earth's history. Paleontologists study fossils (remains of ancient life) for evidence of the evolution of life on Earth. Fossils not only relate evolution, but also speak of the environment in which the organism lived. Corals in rocks at the top of the Grand Canyon in Arizona, for example, show a shallow sea flooded the area around 290 million years ago. In addition, by determining the ages and types of rocks around the world, geologists piece together continental and oceanic history over the past few billion years. Plate tectonics (the study of the movement of the sections of Earth's crust) adds to the story with details of the changing configuration of the continents and oceans.

Many other sciences also contribute to geology. The study of the chemistry of rocks, minerals, and volcanic gases is known as geochemistry. The physics of Earth is known as geophysics. Paleobotanists study fossil plants. Paleozoologists reconstruct fossil animals, while paleoclimatologists reconstruct ancient climates.

Environmental geologists attempt to minimize both the human impact on Earth and the impact of natural disasters on human kind. Hydrology and hydrogeology, two subdisciplines of environmental geology, deal specifically with water resources. Hydrologists study surface water whereas hydrogeologists study ground water. Both disciplines try to reduce the impact of pollution on these resources. Economic geologists focus on finding the minerals and fossil fuels (oil, natural gas, coal) needed to maintain or improve global standards of living.

[See also Geologic map ]

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ge·ol·o·gy / jēˈäləjē/ • n. the science that deals with the earth's physical structure and substance, its history, and the processes that act on it. ∎  the geological features of an area: the geology of the Outer Hebrides. ∎  the geological features of a planetary body: the geology of the surface of Mars. DERIVATIVES: ge·o·log·ic / ˌjēəˈläjik/ adj. ge·o·log·i·cal / ˌjēəˈläjikəl/ adj. ge·o·log·i·cal·ly / ˌjēəˈläjik(ə)lē/ adv. ge·ol·o·gist / -jist/ n. ge·ol·o·gize / -ˌjīz/ v.

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geology Study of the materials of the Earth, their origin, arrangement, classification, change and history. Geology is divided into several categories, the major ones being mineralogy (arrangement of minerals), petrology (rocks and their combination of minerals), stratigraphy (succession of rocks in layers), palaeontology (study of fossilized remains), geomorphology (study of landforms), structural geology (classification of rocks and the forces that produced them), and environmental geology (study of use of the environment).

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geology XVIII. — modL. geōlogia; see GEO-, -LOGY.
So geological, geologist XVIII.

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geology •haji • algae • Angie •argy-bargy, Panaji •edgy, sedgy, solfeggi, veggie, wedgie •cagey, stagy •mangy, rangy •Fiji, gee-gee, squeegee •Murrumbidgee, ridgy, squidgy •dingy, fringy, mingy, stingy, whingy •cabbagy • prodigy • effigy • villagey •porridgy • strategy • cottagey •dodgy, podgy, splodgy, stodgy •pedagogy •Georgie, orgy •ogee • Fuji •bhaji, budgie, pudgy, sludgy, smudgy •bulgy •bungee, grungy, gungy, scungy, spongy •allergy, analogy, genealogy, hypallage, metallurgy, mineralogy, tetralogy •elegy •antilogy, trilogy •aetiology (US etiology), amphibology, anthology, anthropology, apology, archaeology (US archeology), astrology, biology, campanology, cardiology, chronology, climatology, cosmology, craniology, criminology, dermatology, ecology, embryology, entomology, epidemiology, etymology, geology, gynaecology (US gynecology), haematology (US hematology), hagiology, horology, hydrology, iconology, ideology, immunology, iridology, kidology, meteorology, methodology, musicology, mythology, necrology, neurology, numerology, oncology, ontology, ophthalmology, ornithology, parasitology, pathology, pharmacology, phraseology, phrenology, physiology, psychology, radiology, reflexology, scatology, Scientology, seismology, semiology, sociology, symbology, tautology, technology, terminology, theology, topology, toxicology, urology, zoology • eulogy • energy • synergy • apogee • liturgy • lethargy •burgee, clergy •zymurgy • dramaturgy

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