Shaler.] 198 [January 19, 



stratification. There are, however, certain features which distinguish 

 this mass from the ordinary moraines, such as may be found in con- 

 tact with existing glaciers in Switzerland, or in lower positions in 

 the valleys of the same region, where similar accumulations mark the 

 successive stages of retreat of the ancient ice streams. There is a 

 much greater uniformity in the condition of the materials; a far 

 larger part of the boulders, amounting to about two or three per 

 cent., are distinctly scored, or scratched. At certain points, though 

 the paste still envelops the pebbles, there is a certain bedding to the 

 mass, produced by pebbles of a similar size being more abundant on 

 particular levels. On the very summits of these drift ridges, we gen- 

 erally find the large boulders very abundant; indeed it seems at first 

 as if there had been some peculiar change in the conditions of de- 

 position at the time when these boulders Avere accumulated. A care- 

 ful examination has convinced me that in most cases these abundant 

 erratics on the summits of the hills are the remains of that part of 

 the section which has disappeared since the formation of these ridges. 

 A comparison of the frequency of occurrence of these boulders in the 

 remaining parts of the hills and on the surface, will satisfy any one 

 that there must have been a very large amount of denudation since 

 their formation. With this sort of a measure we cannot suppose that 

 the amount of height lost by these hills has been much less than one 

 hundred feet. 



Should the student feel any doubt concerning the essentially un- 

 stratified character of these drift beds, he has only to compare the 

 sections exposed around the base of many of these ridges where the 

 same materials which once formed a part of the mass of the hills have 

 been worn away and stratified by the action of the sea at a time 

 when the emergence of the land at the close of the glacial period 

 had not been completed. He will there see that the pebbles are all 

 deposited separately from the sand, and this in turn apart from the 

 mud, the order of the deposits being precisely that which is always 

 found where such varied materials are acted upon in the tidal cur- 

 rents which sweep every sea shore. Although at first disposed not to 

 accept that view, I have been compelled by an extensive study of 

 these drifts to adopt the theory advanced by Agassiz, that these 

 drift deposits are essentially the work of some other agent of deposi- 

 tion than water. I see no other view likely to meet these facts than 

 that offered by Professor Agassiz, i. e., that this mass is the material 

 which rested in and upon the glacial sheet at the close of its history 



