ABSTRACT
Although Davis constantly acknowledged his debt to such predecessors as Powell, Jukes, Dutton and Gilbert, in later life he came to refer to his first notion of the cycle of erosion, while working on the Northern Pacific Railroad Survey in Montana in 1883, as rather like the blinding flash of understanding experienced by a prophet in the wilderness. Indeed, depressed by President Eliot’s letter he must have pictured himself something of an outcast. As already mentioned in Chapter 8, Davis never forgot his mood of this period and kept a copy of Eliot’s letter for the rest of his life (see also Volume I, pp. 621–41). He took every opportunity of reminding his Harvard audiences of Eliot’s decision to terminate his appointment, a decision which Davis’ later eminence seemed to ridicule. However, at the age of thirty-three on the high plains of Montana with no substantial publications to his name and the threat of dismissal hanging over him, Davis was perhaps in a receptive mood for the idea which was to dominate and mould his academic life.
In the spring of 1883 I had a very discouraging letter from President Eliot, in which he said that my chance of promotion at Harvard was small and that I had better look elsewhere for it. By great good fortune my old teacher Raphael Pumpelly invited me to spend the summer of that year in Montana, where he was in charge of the Northern Transcontinental Survey for the Northern Pacific Railroad. I went out there with the idea that the Plains of eastern Montana were smooth because they had recently emerged from the sea in which their strata had been laid down. To my great surprise it was soon discovered that the Plains were fairly smooth because they had been almost completely worn down from a much greater original altitude; not down to sea level, but to so small an altitude that their rivers had gentle fall; also that since that their down-wearing their rivers had begun again to cut new valleys in consequence of some change, perhaps a small new uplift. The evidence for this conclusion was, first, the repeated occurrence of low outcrop scarps of faintly inclined resistant strata, all of which had been worn back from their original extension. Second, the occurrence of several dike walls from 100 to 500 feet in undulating height; they must have been enclosed when driven up for otherwise their lava would have spread over the Plains far and wide. Third, the presence of several lava-capt mesas, which evidently represented slight hollows in the land surface at the time of the outflow of their lava, and which survived today over the lower land worn down where not lava protected. Fourth, the Crazy Mountains, which stand 3000 or 4000 feet above the plains, because their nearly horizontal strata are knit together by a multitude of dikes. Davis (4th from left) on an unknown (European?) field trip https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9780203472538/8f31c45d-fefa-4125-8bb1-ea2af857126d/content/fig27_B.jpg" xmlns:xlink="https://www.w3.org/1999/xlink"/> (Courtesy R. Mott Davis) Davis examining a volcano. https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9780203472538/8f31c45d-fefa-4125-8bb1-ea2af857126d/content/fig28_B.jpg" xmlns:xlink="https://www.w3.org/1999/xlink"/> (Courtesy Howard M. Turner, Boston)
It was thus forced upon me that the plains are old, not young; also that young valleys are now incised in the old plains because of revived erosion by their rivers. The scheme of the cycle of erosion, published in the following year, was a natural outcome of this summer’s observations. The following years at Harvard I introduced the natural history of rivers into my course on physical geography, and thus enlivened what had been before a very dull topic.
(Comment by Davis, written for Rigdon, 1933, pp. 65–6)