290 JET AT. 29. [1838, 



He started, towards the end of June, on his expedition to 

 Glen Roy, of which he writes to Fox : " I have not been 

 very well of late, which has suddenly determined me to leave 

 London earlier than I had anticipated. I go by the steam- 

 packet to Edinburgh, take a solitary walk on Salisbury Craigs, 

 and call up old thoughts of former times, then go on to 

 Glasgow and the great valley of Inverness, near which I intend 

 stopping a week to geologise the parallel roads of Glen Roy, 

 thence to Shrewsbury, Maer for one day, and London for 

 smoke, ill-health and hard work." 



He spent "eight good days" over the Parallel Roads. His 

 Essay on this subject was written out during the same summer, 

 and published by the Royal Society.* He wrote in his Pocket 

 Book: "September 6 [1838]. Finished the paper on 'Glen 

 Roy,' one of the most difficult and instructive tasks I was ever 

 engaged on." It will be remembered that in his ' Recollec- 

 tions ' 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 

 formation 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 alluvium. 

 In, arguing against this theory he conceived that he had dis- 

 proved 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 hypothesis 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 

 character of my father's Glen Roy work : 



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

 * < Phil. Trans.' 1839, pp. 39-82. 



