310 On the Erosion of Valleys and Lakes, 



solely in the sea by the transporting agency of icebergs. Let 

 those who still believe it refer for proof to the contrary to Mr. 

 Geikie's admirable work i On the Phenomena of the Glacial Drift 

 of Scotland/ I know enough of the superficial strata in North 

 America to foresee that the erratic deposits there will some day 

 also be divided into terrestrial and marine series, and I am 

 pretty sure that Sir William Logan will not deny the proba- 

 bility. For the vast size of the ancient glaciers of that con- 

 tinent, I would refer to Professor Dana's admirable Manual of 

 American Geology. It is a mistake to suppose that the stria- 

 tums there merely run from north to south, for Sir William 

 Logan, who has mapped them, proves that they often conform 

 to the bends of the valleys. 



As regards the great lakes of that continent, so far from being 

 " cavities originally due to a combination of ruptures and denu- 

 dations of the rocks," it is impossible intimately to know the 

 country and believe it. There the Silurian strata, amid which 

 the lakes lie, are arranged so tranquilly and at angles so low, 

 that the flattest chalk of Great Britain may be almost said to be 

 tumultuous in comparison ; and the forthcoming sections of Sir 

 William Logan conclusively prove that around the lakes there 

 is no trace of dislocation to help to form the hollows, nor yet do 

 they lie in hollows of special subsidence. Only Lake Superior 

 covers a faint synclinal curve; and Lake Ontario, so far from 

 occupying an area of special depression, actually lies on a very 

 low anticlinal bend of soft strata, the top of which has been 

 denuded away. That Sir William, who has been called the best 

 stratigraphical geologist in America, believes that ice has some- 

 thing to do with the scooping out of rock-basins, any one 

 may see who refers to his late masterly report on the geology of 

 Canada ; and Professor Newberry, whom Sir Roderick knows as a 

 physical geologist and geographer, adheres strongly to that opinion. 



As for the observation of my friend M. de Verneuil, that the 

 orographic hollows in Spain are precisely those that " a theorist " 

 might " attribute to excavation by ice," I decline to be judged 

 by it, till I have seen them and declared that opinion. I object, 

 both for myself and my supporters, that we should be judged in 

 a manner so vague. And further, I think I appeal to Nature 

 to some purpose when, neither for the first nor the second time, 

 I ask philosophers to consider why it is that not only drift- and 

 moraine-dammed lakes, but striated rock-basins of all sizes occur 

 in such prodigious numbers in America, Scandinavia, the High- 

 lands, and in all other rocky temperate regions, high or low, that 

 have been glaciated, while in tropical and subtropical regions 

 they are so rare as to be quite exceptional elsewhere than in 

 mountain areas that now or once maintained their glaciers. 



