Additional discussion of Jamieson's theory that the roads of Glen Roy were formed by a glacial lake. Suggests the possible marine origin of the Glen Spean terraces. Comments on the power of lakes to produce pebbles. Discusses elevation of Wales and Scotland during the glacial period.
Down Bromley Kent
My dear Lyell
I have read M
If the Lochaber Lakes had been formed by a ice-period posterior to the
(marine?) sloping terraces in the Spean; would not
But it is folly my scribbling thus.— You have a grand problem, &
Heaven help you & M
Ever my dear Lyell | Yours truly | C. Darwin
(This is dreadfully untidy & useless, but I am too tired to rewrite it.—)
- f1 3260.f1The reference is to Thomas Francis Jamieson's letter to Lyell, 19 September 1861 (see Correspondence vol. 9, Appendix IX).
- f2 3260.f2Jamieson had written: `I see no difficulty at present in allowing that the sea might have occupied Glen Spean &c after the era of these lakes up to 500 or 600 feet above the present coast line, in which case these accumulations might be partly of marine origin.' (see Correspondence vol. 9, Appendix IX). CD discussed this point in his paper, `Notes on the effects produced by the ancient glaciers of Caernarvonshire, and on the boulders transported by floating ice', published in the Edinburgh New Philosophical Journal 33 (1842): 352--63 (Collected papers 1: 163--71). Andrew Crombie Ramsay espoused the view that there had been a period of glacial activity in Wales after the deposition of marine drift (Ramsay 1852, p. 376).
- f3 3260.f3See CD's Glen Roy notebook, pp. 31--2 (Notebooks), in which he noted that the sloping terraces of Glen Spean were `difficult to explain on <formation> deposition in lake'. In his paper on the `parallel roads' of Glen Roy, CD described the accumulation of `alluvial' gravels and other debris that formed flat-topped `buttresses' below the level of the lowest `road' in Glen Spean. He argued that if the valley had been filled with an arm of the sea, into which the river transported its debris, and if the land was rising in a succession of short steps, the river would have deposited its material in deltaic form. Therefore, as the sea retreated from the valley, the river would erode a gorge through material previously deposited and, at the same time, deposit more material further downstream at the point where it entered the sea at its new, lower level. With this account, CD believed he had demonstrated the case for a gradual fall of the level of water in Glen Spean from the lowermost `road' towards the present sea level. See `Observations on the parallel roads of Glen Roy, and of other parts of Lochaber in Scotland, with an attempt to prove that they are of marine origin' (Collected papers 1: 89--137); see also Rudwick 1974, pp. 121--4.
- f4 3260.f4CD mentioned this observation in his paper on the ancient glaciers of Caernarvonshire, North Wales, p. 354 (see n. 3, above).
- f5 3260.f5See South America, p. 79.
- f6 3260.f6In his work on Glen Roy and other geological phenomena, CD based his ideas on Lyell's theory of crustal elevation and subsidence as the vera causa of the phenomena. For a discussion of CD's work on Glen Roy within the context of his wider conception of natural history, see Rudwick 1974, pp. 153--74.