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



observations ; for the extreme end of the petty glaciers of to-day 

 have only a small erosive power, and not one that I know in the 

 Alps has ever in historical times been protruded in mass on and 

 well over a plain. When a glacier lies on a slope, it needs little, 

 reflection to show that its tendency will by no means be to pro- 

 duce " cup-and-saucer-shaped cavities "** 



The argument that the constant occurrence of transverse 

 rents in the same part of a glacier proves that the ice " cannot 

 saw through and get rid of the obstacles which impede the free- 

 dom of its onward march," reads strangely after the admission 

 that " everywhere we behold proofs that the glacier, by the aid 

 of sand and pebbles, can grind down, polish, and plane the 

 bottom." Neither the mountains that bound nor the valleys 

 under the glaciers can possibly preserve the same relative de- 

 tails of feature till all shall be worn away ; and the position of 

 the obstacles as constants can no more be considered indestruc- 

 tible than the Falls of Niagara, which Sir Charles Lyell has long 

 ago shown may retreat till Lake Erie itself shall be drained. 



Another point seems to require explanation. At the beginning 

 of the subject (p. 168) it is stated that lakes are exceedingly 

 common in all regions that have been glaciated, and rare in tro- 

 pical and subtropical regions; and at page 170 it is observed 

 that " such basins, large and small, are met with in all latitudes." 

 Now I have specially guarded myself against being supposed to 

 assert that all lake-basins have been formed by ice ; but if " such 

 basins, large and small, are met with in all latitudes," which I 

 doubt (except among mountains which maintain or have main- 

 tained glaciers), their relative proportions in different lati- 

 tudes deprives the argument of much or of any value; and for 

 other reasons the same may be said of the remark " that there 

 are lacustrine deposits of all geological epochs , attesting the 

 existence of lakes at times when no one is disposed to attribute 

 them to the agency of ice." There may have been lakes of all 

 geological epochs ; but I should like to see proofs adduced; and 

 very few of them are mentioned in the ' Elements/ Where 

 are the lakes of the Silurian strata, which themselves embrace 

 more epochs than one, if unconformities constitute epochs ? 

 And though Sir Charles compares the Old Red Sandstone fish to 



* See my paper " On the Erosion of Valleys and Lakes/' Phil. 

 Mag. October 1864. I have often thought that the absence or scarcity 

 of lakes on the southern flanks of the Himalayan is due to the well-known 

 steepness of the valleys, and their occurrence in numbers on the north is 

 owing to the opposite circumstance. Tarns I know there are on frag- 

 mentary flats on the mountains on the south side. But I can only judge 

 from maps and descriptions, and therefore dare not positively assert it. 

 After the publication of my first memoir, Dr. Hooker wrote me a letter 

 confirmatory of these views, which were till then new to him. 



