Maclure, William

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Maclure, William

(b. Ayr, Scotland, 27 October 1763; d. St. Angelo, Mexico, 23 March 1840)


Maclure, the son of David and Ann Maclure, was educated by private tutors. He came to the United States in 1782 to establish “mercantile arrangements” and returned to London as a partner in the house of Miller, Hart and Company, where he soon amassed a fortune. He traveled back and forth between Europe and America, and spent several years traveling through Europe, including Scandinavia and Russia, observing geological features and seeking instruction from geologists in several countries. In Paris he met Count Volney, who discussed American geology with him.

Returning to the United States in 1796, Maclure examined the geology of the country as he traversed it from New England to the far southeast, “crossing the dividing lines of the principle formations in 15 or 20 different places.’“He published his report and colored map, “Observations on the Geology of the United States, Explanatory of a Geological Map“(in Transactions of the American Philosophical Society,6 [1809], 411–428).

In 1815 Maclure visited France and met Lesueur the painter-naturalist, whom he persuaded to return to America with him as his personal cartographer-naturalist. They spent the winter of 1815–1816 examining the geology and natural history of the West Indies, then made repeated traverses of the Allegheny Mountains, collecting specimens and revising the geological map. From December 1817 to April 1818, Maclure organized an expedition to Georgia and Spanish Florida with Lesueur, Thomas Say, Titian Peale, and George Ord.

Maclure developed an estate in Spain and lived there from 1820 to 1824. In 1824, following a revolution and the confiscation of his property, he returned to America. Here he joined Robert Owen in his New Harmony venture, in which he invested $82,000. He visited Mexico in 1827 and later moved there.

Maclure’s best known work is the Observations on the Geology of the United States. Although preceded by Johann D, Schopf’s work in German (1787) and Volncy’s in French (1803), Maclure’s articles and book are the first connected account originally written in English on the geology of the United States. The expanded and revised work and map were published as a separate volume in 1817 and in the Transactions of the American Philosophical Society in 1818. In the text and map, Maclure divided the country into areas of “primitive rocks,” “transition rocks,” “floetz and secondary rocks,” and “alluvial rocks.” The primitive rocks are crystalline rocks in the area that extends from New England southwest to Alabama. The transition rocks occur in the folds of the Appalachians; the secondary rocks are the flat-lying strata west of the Appalachians. The alluvial rocks are found in the valley of the Mississippi and in the coastal plain from Cape Cod southeast to the mouth of the Mississippi River.

In 1817 Maclure published a report on his detailed examination of the West Indies (Journal of the Academy of Natural Sciences of Philadelphia,1, 134–149). In this report he discussed the uplifted coral limestone in some of the islands and the various kinds of volcanic materials, including volcanic breccia, which he interpreted as volcanic mud flows. His “Essay on the Formation of Rocks …” (1818) is important for his explanation of his terminology and for his theories of the origin of rocks. In a series of eleven papers (1819–1831) published in the AmericanJournal of Science, Maclure recorded observations on the geology of the United States and other parts of the world and expanded upon his ideas of rock origin and geological processes.

The short paper “Genealogy of the Earth-Geological Observations” (1838) is the most philosophical of his geological writings. In it he espoused Lamarckian evolution and clarified his belief in organic and inorganic development through a gradual series of minute changes, rather than by large jumps or catastrophes,

Maclure is usually regarded as a follower of Werner because he used that terminology, but he specifically disclaimed his belief in that school’s theory of crystalline rock origin. He was convinced of the igneous origin of basalt and stated that sedimentary rocks were deposited in separate basins and were therefore not continuous in an “onionskin” fashion around the world. He was uncertain about the origin of primitive rocks, and thought that they might be diverse in origin. From his studies of various areas of the world, he had concluded that sedimentary rocks and lava flows alternated with each other. Thus he speculated that the primitive rocks may have originated as sediments and lava, later becoming “smelted, roasted and liquified,” almost the concept of granitiza-tion in present-day terminology.

Maclure was convinced that basalt and related rocks developed from lava flows, but he did not discuss granites as intrusive rocks, nor did he mention the explanations of Hutton and Playfair. He urged more attention to the “primitive formations” because of their great age and the changes that they had undergone. He disclaimed support, however, of the aqueous theory of the origin of primitive rocks. “The geology of the United States … is a strong argument against the Wernerian system—all these theories have had their day, and are fast going out of fashion” (1822).

Maclure recognized the role of streams in the formation of valleys. Following S. L. Mitchill and many others, he thought that the region west of the Appalachian Mountains had once been the site of a great lake, which had drained out through the Hudson and broken out across the mountains in several other valleys. Maclure was one of the first men in America to notice and speculate on the origin of the granite erratics in the northern part of the country. He stated that the granite erratics between Lake Erie and the Ohio River had been transported southward by “large pieces of floating ice” in the lake that he believed had occupied the trans-Appalachian area (1823).

Maclure’s work on metallic deposits and the connection between metals and volcanic regions are of interest. In writing about Mexico (1831), he proposed that “precious metals have been converted into vapor, that would penetrate through chinks that would not permit lava to pass.” Thus he realized that lava was intrusive until it reached the surface. This explanation for veins is directly contrary to that of Werner, who supposed that veins had been formed by infilling of cracks from the surface.

Maclure’s influence was not only great as an observer and writer on geology and as a maker of important maps, but also through his support of scientists and scientific organizations. One of the founders of the Academy of Natural Sciences of Philadelphia, he was president from 1817 to his death.


I. Original Works. Maclure’s map and Observations of 1817 have been produced in facsimile (New York, 1962). The 1809 map has been reproduced by Merrill (New Haven, 1924). His papers on his travels are in the early volumes of the American Journal of Science and the Journal of the Academy of Natural Sciences of Philadelphia. Among them are “Essay on the Formation of Rocks …,” in Journal of the Academy of Natural Sciences of Philadelphia,1 (1818), and published separately (Philadelphia, 1818; New Harmony, 1832).

The three-volume work Opinions on Various Subjects Dedicated to the Industrious Producers(New Harmony, 1831–1838) sets forth in detail his ideas on economic, political, and related areas; it contains little science except for one important paper, “Genealogy of the Earth-Geological Observations,” ibid., III, 175–178.

II. Secondary Literature. There is as yet no full biography of Maclure. S. G. Morton, A Memoir of William Maclure, Esq. (Philadelphia, 1841), with a portrait, reprinted in American Journal of Science,47 (1844), 1–17, is the source of the most immediate information. A. E. Bestor, “Education and Reform at New Harmony: Correspondence of William Maclure and Marie Duclos Fretageot, 1820–1833,” in Indiana Historical Society,15, no. 3 (1948), discusses Maclure’s association with New Harmony and contains some of the letters from Europe and Mexico preserved at the Working Men’s Institute at New Harmony; Charles Keyes, “William Maclure: Father of American Geology,” in Pan-American Geologist,44 (1925), 81–94, is a fulsome account with some information; G. P. Merrill, First One Hundred Years of American Geology (New Haven, 1924; New York, 1962), 31–37, 46–47, has summarized Maclure’s geological contributions; and Jessie Poesch, Titian Ramsey Peale,1799–1885 … (Philadelphia, 1961), gives information on Maclure’s expedition to Georgia and Florida based on original correspondence.

Lesueur’s connection with Maclure is given in some detail by R. W. G. Vail, The American Sketchbooks of Charles Alexander Lesueur 1816–1837 (Worcester, 1938). A portrait of Maclure and many references to his association with Thomas Say are in H. B. Weiss and G, M. Zeigler, Thomas Say, Early American Naturalist (Springfield-Baltimore, 1931). William E. Wilson, The Angel and the Serpent, the Story of New Harmony (Bloomington, Indiana, 1964), gives extensive consideration to Maclure at New Harmony.

All of Maclure’s geological papers are being prepared for publication in facsimile, edited and annotated by George W. White.

George W. White

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Maclure, William

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