298 Prof. A. C. Ramsay on the Glacial Theory of Lake-Basins. 



occupancy, therefore, of cavities by ice, by preventing fluviatile 

 and lacustrine deposition, is one cause of the abundance of lakes 

 which will come into existence whenever the climate changes 

 and the ice melts." After so many ifs, and shoulds, and may 

 he's, I submit that may be one cause, instead of is one cause, 

 would have been a more appropriate mode of expression. These 

 suppositions are backed by the additional statement, that if 

 " we observe a capricious distribution of lake-basins, we have no 

 reason to feel surprise, so long as we conceive the origin of such 

 basins to be due to subterranean movements in the earth's 

 crust ; for these may be partial in their extent, or may vary in 

 their direction in a manner which has no relation to the course 

 of the valleys." I prefer to so many surmises the simplicity of 

 my hypothesis, that as glacier-ice does erode the rocky floor over 

 which it passes, and as it can, under certain circumstances, move 

 up slopes, the nature of that erosion will be, and was dependent, 



1. On the angles of the slopes over which it passed, when 

 these slopes were seriously appreciable. 



2. On the fact that the glaciers sometimes passed from these 

 slopes into low grounds, into which the great old glacier-valleys 

 opened. 



3. That at the mouths of these great old valleys, and some- 

 times near their mouths, where two or more great glaciers met, 

 the downward pressure of all the accumulated ice of all the 

 tributary valleys would be greatest. 



4. For, because of its inertness in such flat ground, the 

 grinding-power of the ice urged on from behind would be 

 greatest, in accordance with all known physical laws ; and 



5. That, as it progressed and melted, the ice must have been 

 thinner, and must have exercised less erosive power than where 

 it was thick, whence the gradual slope of the bottom of these 

 lakes towards their outflows. 



Sir Charles does not deny that glacier-ice may move up a 

 slope. His idea of tilting supposes it, for the lake-hollows 

 were not filled up with sediments, because they were filled with 

 ice; but, apart from this, on one side there is immense compli- 

 cation of phenomena, which, to meet his case, must be applied to 

 all the mountain- chains and clusters I have ever seen, and, as 

 far as I know, to all of them I have ever read about, and, besides, 

 to all the length and breadth of the northern half of North Ame- 

 rica, while on my side there is, at all events, simplicity. 



As for the surmise that icebergs are likely to hollow out lake- 

 basins of any importance in solid rocks, I have already discussed 

 the subject ; and it is so immaterial to the main argument, and 

 seems to me so utterly improbable, that I will not at present 

 renew the discussion. 



