18411880] GLEN ROY l8l 



theory of Agassiz and Buckland x : until I read your im- Letter 521 

 portant discovery of the outlet in Glen Glaster 2 I never 

 thought this theory at all tenable. Now it appears to me 

 that a very good case can be made in its favour. I am not, 

 however, as yet a believer in the ice-lake theory, but I tremble 

 for the result. I have had a good deal of talk with Mr. Lyell 

 on the subject, and from his advice I am going to send a letter 

 to the Scotsman, in which I give briefly my present impression 

 (though there is not space to argue with you on such points 

 as I think I could argue), and indicate what points strike me 

 as requiring further investigation with respect, chiefly, to the 

 ice-lake theory, so that you will not care about it. ... 



P.S. Some facts mentioned in my Geolog. of S. America, 

 p. 24, 3 with regard to the shoaling of the deep fiords of 

 T. del Fuego near their mouths, and which I have remarked 

 would tend, with a little elevation, to convert such fiords into 

 lakes with a great mound-like barrier of detritus at their 

 mouths, might, possibly, have been of use to you with regard 

 to the lakes of Glen Roy. 



To C. Lyell. Letter S22 



Down, Wednesday, Sth. 



Many thanks for your paper. 4 I do admire your zeal on 

 a subject on which you are not immediately at work. I will 



1 Agassiz and Buckland believed that the lakes which formed the 

 " roads " were confined by glaciers or moraines. See " The Glacial 

 Theory and its Recent Progress," by Louis Agassiz, Edinb. New Phil. 

 Journ., Vol. XXXIII., p. 217, 1842 (with map). 



2 Mr. Milne discovered that the middle shelf of Glen Roy, which 

 Mr. Darwin stated was " not on a level with any watershed " (Darwin, 

 Joe. 67?., p. 43), exactly coincided with a watershed at the head of Glen 

 Glaster (Milne, loc. tit., p. 398). 



3 The creeks which penetrate the western shores of Tierra del Fuego 

 are described as " almost invariably much shallower close to the open 

 sea at their mouths than inland. . . . This shoalness of the sea-channels 

 near their entrances probably results from the quantity of sediment 

 formed by the wear and tear of the outer rocks exposed to the full force of 

 the open sea. I have no doubt that many lakes for instance, in Scotland 



which are very deep within, and are separated from the sea appa- 

 rently only by a tract of detritus, were originally sea-channels, with banks 

 of this nature near their mouths, which have since been upheaved " (Geol. 

 Obs. S. America, p. 24, footnote). 



4 " On the Ancient Glaciers of Forfarshire." Proc. Geol. Soc., Vol. III. 

 p. 337, 1840. 



