WALKER, JOHN

(b. Edinburgh, Scotland, 1731; d. Edinburgh, 31 December 1803), geology, botany, religion.

Walker was born into a family firmly convincted of the value education. His father was rector of the Canongate Grammar School; and as a youth Walker was trained in Latin and Greek, reading in those languages at an early age. In addition to his ability in the classics, he developed an interest in minerals before he was fifteen. After finishing studied at his father’s school, Walker studied at the University of Edinburgh, where he prepared for the ministry in the (Presbyterian) Church of Scotland.

In the course of his work, Walker became especially interested, through the influence of William Cullen, in chemistry and mineralogy. He soon realized that the classification of minerals had been sadly neglected and therefore traveled throughout the British Isles, sometimes with Cullen, collecting minerals from mines and rock outcrops. Using his own collection as well as that at the University Museum, he had established an “elementa mineralogiae” by the 1750’s: this classification was later modified to include 323 genera. Among the most interesting of the minerals that he collected in the 1760’s was strontianite, from the mines of Leadhills.

Licensed to preach in 1754, Walker was assigned to his first post at Glencorse in September 1758. He soon met Henry Home, Lord Kames, who became his enthusiastic sponsor. Through this relationship Walker was commissioned to make an extensive study of the Hebrides in 1764. This was neither his first nor his last study of the Hebrides or the Highlands; and it was directly responsible for the preparation of a two-volume book printed posthumously in 1808 by his friend Charles Stewart.

From his first ministry in 1758 until his appointment in 1779 to the chair of natural history at the University of Edinburgh, Walker spent all of his spare time in the study of botany and geology; and his knowledge of Latin and Greek permitted him to read the significant literature in those fields. Walker was greatly influenced by the works of Cronstedt and especially by the contributions of Linnaeus. with whom he corresponded in the 1760’s.

Most of Walker’s botanical and geological papers were published or prepared between 1758 and 1779. A new phase in his life commenced with his appointment as regius professor at the University of Edinburgh, where his first class was enrolled at least as early as 1781.

Walker was an organizer of the Royal Society of Edinburgh and was appointed first secretary of the Physical Section in 1783; he also was active in the organization of the Natural History Society of Edinburgh in 1782. He was a long-time member of the Highland Society of Scotland and, as a result of his great interest in agriculture, formed the Agriculture Society of Edinburgh in 1792. These groups gave him an opportunity to participate in scientific discussions and provided an outlet for the publication of some of his articles.

In his initial lecture to his first class, Walker said: “I am to teach a science I never was taught.” He then proceeded to organize a set of lectures on geology “or the Natural History of the Earth.” From then until the end of his life he gave regular lectures on the various aspects of geology and had a great influence in establishing the science as a discipline in higher education. Three of his most famous students were James Hall, John Playfair, and Robert Jameson. In addition, he influenced the early development of geology in America through his student Samuel Latham Mitchill, who became one of the leading men of American science upon his return to the New York area. Walker was a contemporary of James Hutton, and both were members of the Royal Society.

One of Walker’s cheif contributions was the establishment of geology as an organized classroom subject in an institution of higher learning, and he therefore has a legitimate claim to the title of “Father of Geological Education.” Walker’s classroom methods were essentially those used today: he lectured; distributed syllabuses; established a laboratory; and brought in rocks, minerals, and fossils, which were studied with a microscope. The laboratory work included the study of polished surfaces and a large suite of minerals and fossils. In the study of minerals he used a hardness scale similar to that devised by Mohs thirty years later.

In his lectures Walker discussed the origin of carbonates and differentiated between limestone and marble. In addition, he considered the origin of igneous and sedimentary rocks. Among the common rocks, he paid particular attention to the origin of basalt and granite and to the environment of deposition of such sediments as sand.

One of his classic works was his essay on peat, in which he made an exhaustive analysis of the organic content and origin of this substance. In other papers he affirmed that petroleum occurred in rocks as a natural substance. His discussion of rock structures included accurate definitions of strike and dip as well as recognition of hoirizontal strata overlying titled beds, a condition to which he referred as offlap. Walker described the work of both surface and subsurface water and recognized density stratification of lake water. He wrote about till but did not know of its glacial origin.

Walker collected fossils and used them for demonstration purposes in the laboratory. He classified the methods of fossilization and strongly supported the Linnaean system of binomial nomenclature. He believed that fossils could be used to determine rock chronology and maintained that animals and plants were linked in a common evolutionary chain from the “lowest subject up to the human species…all being linked…by the most beautiful and regular gradation.”

BIBLIOGRAPHY

Walker’s writings include “An Essay on Peat, Containing an Account of Its Origin, of Its Chymical Principles and General Properties,” in Prize Essays and Transactions of the Highland Society of Scotland, 2 (1803), 1–137; An Economical History of the Hebrides and Highlands of Scotland, 2 vols. (Edinburgh, 1808); Essays on Natural History and Rural Economy (Edinburgh, 1808; repr. London, 1812), published by Charles Stewart; and Harold W. Scott, ed., Lectures on Geology by John Walker (Chicago, 1965), with a complete bibliography, including MSS.

Two short biographies of Walker are W. Jardine, “Memoir of John Walker, D.D.” in The Birds of Great Britain and Ireland, III (London, 1842), 3–50; and George Taylor, “John Walker, D.D., F.R.S.E., 1731-1803, A Notables Scottish Naturalist,” in Transactions of the Botanical Society of Edinburgh, 38 (1959), 180–203. A portrait is in John Kay, A Series of Original Portraits and Caricature Etchings, III (Edinburgh, 1840), 178.

Harold W. Scott