1838.] . GLEN ROY. 261 



on ' Glen Roy,' one of the most difficult and instructive tasks 

 I was ever engaged on." It will be remembered that in his 

 * Recollections ' he speaks of this paper as a failure, of which 

 he was ashamed. 



At the time at which he wrote, the latest theory of the for- 

 mation of the Parallel Roads was that of Sir Lauder Dick 

 and Dr. Macculloch, who believed that lakes had anciently 

 existed in Glen Roy, caused by dams of rock or allu- 

 vium. In arguing against this theory he conceived that 

 he had disproved the admissibility of any lake theory, 

 but in this point he was mistaken. He wrote (Glen Roy 

 paper, p. 49) '* the conclusion is inevitable, that no hypo- 

 thesis founded on the supposed existence of a sheet of 

 water confined by barriers^ that is a lake, can be admitted 

 as solving the problematical origin of the parallel roads of 

 Lochaber," 



Mr. Archibald Geikie has been so good as to allow me to 

 quote a passage from a letter addressed to me (Nov. 19, 1884) 

 in compliance with my request for his opinion on the charac- 

 ter of my father's Glen Roy work : — 



" Mr. Darwin's * Glen Roy ' paper, I need not say, is 

 marked by all his characteristic acuteness of observation and 

 determination to consider all possible objections. It is a 

 curious example, however, of the danger of reasoning by a 

 method of exclusion in Natural Science. Finding that the 

 waters which formed the terraces in the Glen Roy region 

 could not possibly have been dammed back by barriers of 

 rock or of detritus, he saw no alternative but to regard them 

 as the work of the sea. Had the idea of transient barriers 

 of glacier-ice occurred to him, he would have found the diffi- 

 culties vanish from the lake-theory which he opposed, and he 

 would not have been unconsciously led to minimise the alto- 

 gether overwhelming objections to the supposition that the 

 terraces are of marine origin." 



It maybe added that the idea of the barriers being formed 

 by glaciers could hardly have occurred to him, considering 

 what was the state of knowledge at the time, and bearing in 



