18411880] GLEN ROY 173 



failure" ; he argued in favour of sea action as the cause of the terraces 

 " because no other explanation was possible under our then state of 

 knowledge." Convinced of his mistake, Darwin looked upon his error 

 as "a good lesson never to trust in science to the principle of exclusion." 1 



To C. Lyell. Letter 517 



[March gth, 1841.] 



I have just received your note. It is the greatest pleasure 

 to me to write or talk Geology with you. . . . 



I think I have thought over the whole case without 

 prejudice, and remain firmly convinced they [the parallel 

 roads] are marine beaches. My principal reason for doing 

 so is what I have urged in my paper, 2 the buttress-like 

 accumulations of stratified shingle on sides of valley, especially 

 those just below the lowest shelf in Spean Valley. 



2nd. I can hardly conceive the extension of the glaciers 

 in front of the valley of Kilfmnin, where I found a new 

 road where the sides of Great Glen are not very lofty. 



3rd. The flat watersheds which I describe in places where 

 there are no roads, as well as those connected with " roads." 

 These remain unexplained. 



I might continue to add many other such reasons, all of 

 which, however, I daresay would appear trifling to any one 

 who had not visited the district. With respect to equable 

 elevation, it cannot be a valid objection to any one who thinks 

 of Scandinavia or the Pampas. With respect to the glacier 

 theory, the greatest objection appears to me the following, 

 though possibly not a sound one. The water has beyond 

 doubt remained very long at the levels of each shelf this is 

 unequivocally shown by the depth of the notch or beach 

 formed in many places in the hard mica-slate, and the large 

 accumulations or buttresses of well-rounded pebbles at certain 

 spots on the level of old beaches. (The time must have been 

 immense, if formed by lakes without tides.) During the 

 existence of the lakes their drainage must have been at 

 the head of the valleys, and has given the flat appearance 

 of the watersheds. All this is very clear for four of the 

 shelves (viz., upper and lower in Glen Roy, the Sooft. one 



1 Life and Letters, I., p. 69. 



2 " 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.' 3 Phil. Trans. R. Soc., 1839, p. 39. 



