172 GEOLOGY [CHAP. IX 



physical feature were those of MacCulloch l and Sir Thomas Lauder 

 Dick, 2 in which the writers concluded that the roads were the shore-lines 

 of lakes which once filled the Lochaber valleys. Towards the end of 

 June 1838 Mr. Darwin devoted "eight good days" 3 to the examination 

 of the Lochaber district, and in the following year he communicated 

 a paper to the Royal Society of London, in which he attributed their 

 origin to the action of the sea, and regarded them as old sea beaches 

 which had been raised to their present level by a gradual elevation 

 of the Lochaber district. 



In 1840 Louis Agassiz and Buckland 4 proposed the glacier-ice theory ; 

 they described the valleys as having been filled with lakes dammed back 

 by glaciers which formed bars across the valleys of Glen Roy, Glen 

 Spean, and the other glens in which the hill-sides bear traces of old 

 lake-margins. Agassiz wrote in 1842: "When I visited the parallel 

 roads of Glen Roy with Dr. Buckland we were convinced that the glacial 

 theory alone satisfied all the exigencies of the phenomenon." 5 



Mr. David Milne (afterwards Milne-Home) 6 in 1847 upheld the 

 view that the ledges represent the shore-lines of lakes which were 

 imprisoned in the valleys by dams of detrital material left in the glens 

 during a submergence of 3,000 feet, at the close of the Glacial period. 

 Chambers, in his Ancient Sea Margins (1848), expressed himself in 

 agreement with Mr. Darwin's marine theory. The Agassiz-Buckland 

 theory was supported by Mr. Jamieson, 7 who brought forward additional 

 evidence in favour of the glacial barriers. Sir Charles Lyell at first 8 

 accepted the explanation given by Mr. Darwin, but afterwards 9 came 

 to the conclusion that the terrace-lines represent the beaches of glacial 

 lakes. In a paper published in iSyS, 10 Prof. Prestwich stated his accept- 

 ance of the lake theory of MacCulloch and Sir T. Lauder Dick and of 

 the glacial theory of Agassiz, but differed from these authors in respect 

 of the age of the lakes and the manner of formation of the roads. 



The view that has now gained general acceptance is that the parallel 

 roads of Glen Roy represent the shores of a lake " that came into being 

 with the growth of the glaciers and vanished as these melted away." n 



Mr. Darwin became a convert to the glacier theory after the publica- 

 tion of Mr. Jamieson's paper. He speaks of his own paper as " a great 



1 Trans. Geol. Soc., Vol. IV., p. 314, 1817. 



2 Trans. R. Soc. Edinb., Vol. IX., p. i, 1823. 



3 Life and Letters, I., p. 290. 



4 Edinb. New Phil. Journal, Vol. XXXIII., p. 236, 1842. 



5 Ibid., p. 236. 



6 Trans. R. Soc. Edinb., Vol. XVI., p. 395, 1847. 



7 Quart. Journ. Gcol. Soc., Vol. XIX., p. 235, 1863. 



8 Elements of Geology, Ed. II., 1841. 



9 Antiquity of Man, 1863, pp. 252 et seq. 



10 Phil. Trans. R. Soc., 1879, p. 663. 



11 Sir Archibald Geikie, he. cit., p. 269. 



