THOREAU ON MONADNOCK: LONG ON BOTANY AND PHILOSOPHY, SHORT ON GEOLOGY

Thoreau visited Monadnock four times between 1844 and 1860. His journal writings are replete with descriptions of flora, fauna and landforms on the mountain. He described the coarse gravelly soil, the “regularly stratified rocks”, the bogs and the cliffs, which he noted as being mostly on the southeast side. Using the crude method of hurling a stick ahead of him to estimate distances, Thoreau produced a fair map of the mountain with its “buttresses and spurs”. He sketched and measured glacial striae without speculating as to their origin, and noted “large boulders, left just on the edge. . .as if the Titans were in the very act of transporting them when they were interrupted”. He had read Jackson's 1844 account of Monadnock geology (“mica slate and garnet-bearing gneiss”) and was thus likely influenced by Jackson's low opinion of Agassiz' recent hypotheses regarding glacial striae and drift. Even Edward Hitchcock, in his 1856 discussion of "drift unmodified and drift modified", preferred iceberg transport to explain erratics, and glacial theory did not achieve widespread acceptance until the following decade.

Perhaps Thoreau's most original observations have to do with the water budget on Monadnock, centered on the bog which bears his name, where he debated the balance between rain, fog, evaporation, underground springs, and streams flowing away from the Connecticut/Merrimack divide. He described orographic cloud formation in stunning detail. However, he made no mention of the conspicuous sillimanite pseudomorphs after andalusite, which according to Jackson give Monadnock's rocks a “porphyritic appearance”, nor of the great isoclinal fold exposed on the west-facing cliff near the summit. Even more curious, given the Thoreau family pencil business, is the omission of reference to a graphite mine that operated on the mountain from 1847 to 1850! Were any of his visits to Monadnock in part on business at a time when the Thoreaus were expanding their trade in graphite?

The balance of Thoreau's Monadnock journal entries emphasize botany and philosophical musings. He was evidently much more interested in plants and the “science which deals with the higher law” than in geology. Significantly, in declining a membership to the American Association for the Advancement of Science, he described himself as “a mystic, a transcendentalist, and a natural philosopher to boot”, not as a scientist.