(b. Llangwnadl, Carnarvonshire, Wales, 1700; d. New York, N.Y., 11 June 1756)
cartography, geography, geomorphology, geology.
Evans came to Philadelphia sometime before 1736 and became known as surveyor, draftsman, and mapmaker. He also gave lectures on electricity and wrote on climatology. He was a friend and associate of Benjamin Franklin, John Bartram, Governor Thomas Pownall, and Cadwallader Colden, and was very helpful to the visiting Swedish scientist Peter Kalm, who referred to him as “an ingenious engineer.”
Based on his own surveys and explorations he made maps of land tracts and boundaries. His two great published maps are “A Map of Pennsylvania, New-Jersey, New-York, And the Three Delaware Counties” (1749; a revision was published in 1752) and “A General Map of the Middle British Colonies in America” (1755). In the booklet that accompanies the latter map Evans not only describes the geography, geomorphology, and some geology and other natural features of the region, but also makes a vigorous attack on the contemporary permissive policy of the British administrators toward the French encroachment in the Ohio Valley, which he vehemently insists must be preserved for English settlement. After a second fiery pamphlet, which even hinted at treasonous collusion with France, Governor Robert Hunter Morris of Pennsylvania secured Evans’ imprisonment in New York, to which he had moved. He was released from jail only three days before he died, leaving his motherless eleven-year-old daughter to the care of friends.
In 1743 Evans traveled with John Bartram and Conrad Weiser to Lake Ontario. In his journal (published in 1776 by Pownall) he recorded observations on raised beaches of the once higher Great Lakes and speculated penetratingly on the drainage of the earlier lakes and the consequent rise of the land because “This part of America was disburthened of such a Load of Waters.”
Evans filled in the blank spaces of his maps of 1749 and 1752 with notes on weather, roads, streams, and geology. His notes on the Endless (Appalachian) Mountains were not only descriptive but were also the first analysis of their origin, based on the fossils preserved in their strata and on the erosion of valleys from a former plain (peneplain in modern terms) to form the ridges.
Evans’ 1755 “Map of the Middle British Colonies” is partly a geologic map, showing not only the location of economic minerals—“coals,” “freestone,” pottery clay, and petroleum—but also the trends of the mountains and some indication of rock types. He was keenly aware of the three-dimensional nature of geology and constructed map profiles and sections of strata with their “particular fossils” to accompany the map. Evans said, however, that for “want of room in the plate,” these sections would be published on later maps when he had more space. Evans died before these later maps could be published.
The thirty-six-page Analysis of a General Map of the Middle British Colonies... and Description of the Face of the Country... that accompanied the 1755 map contains (in addition to the discussion of the administration of the Ohio Valley) a long and clear statement of the geomorphic and geologic provinces of the eastern United States. In this prototypical work of American geomorphology, divisions now known as the New England Upland, the Coastal Plain, the Fall Line, the Piedmont, the Blue Ridge, the Folded Appalachians, the Allegheny Front, and the Allegheny Plateau are first delineated. Evans realized that these regions were different because of differing rocks and structures.
Evans’ great map was reprinted and copied at least twenty-seven times in the next fifty years. His regional geologic and physiographic classification provided in greater or lesser part the geologic framework for later writers in the sixty years following his death. He was a great cartographer and an early student not only of landscape but also of fossils and the relation of bedrock to surface morphology. He was the first in America to recognize the principles of isostasy.
1. Original Works. Evans’ maps and publications, now very rare, are reproduced in facsimile, with his extensive unpublished notes, in Laurence H. Gipson, Lewi Evans (Philadelphia, 1939). Evans’ 1743 journal is published in Thomas Pownall, A Topographical Description of Such Parts of North America... (London, 1776; Pittsburgh, 1949).
II. Secondary Literature. For Evans’ life and the history of his maps see Gipson, above; H.N. Stevens, Lewis Evans, His Map of the Middle British Colonies (London, 1905, 1924, 1929); and L. C. Wroth, An American Bookshelf (Philadelphia, 1934).
For discussion of Evans’ geological observations see G. W.White, “Lewis Evans’ Early American Notice of Isostasy,” in Science, 114 (1951), 302–303; “Lewis Evans’ Contributions to Early American Geology—1743–1755,” in Transactions of the Illinois Academy of Science, 44 (1951), 152–158; and “Lewis Evans (1700–56): A Scientist in Colonial America,” in Nature, 177 (1956), 1055–1056.
George W. White