10 . SURFACE GEOLOGY. 



While this deposit was thus accumulating beneath the ice, great 

 amounts of material, coarse and fine, were swept away from hill-slopes 

 and mountain sides, and afterwards carried forward in the ice. When 

 this melted, a large portion of the material which it contained fell loosely 

 upon the surface, forming an unstratified deposit of gravelly earth and 

 boulders, which may be called the Upper Till. There is almost always 

 a definite line of separation, at a depth varying from two or three to fif- 

 teen or twenty feet, between the upper and lower till. It will be seen 

 that the upper member is the one usually exposed at the surface, and it 

 is often the only one present where only a thin covering of till is found. 

 Its characteristics are the larger size of its boulders, which are mostly 

 angular and unworn, and commonly derived from less remote localities 

 than the glaciated stones in the lower till; the yellowish or reddish color 

 of its fine detritus, produced by the hydrated ferric oxide to which its 

 iron has been changed by exposure to air and water ; and the compara- 

 tive looseness of its whole mass. This division of the till into two 

 members, which is very well marked throughout New Hampshire, is 

 also conspicuous in Sweden and other parts of Europe ; and the peculiar 

 features of each have been recently pointed out by Dr. Otto Torell, of 

 Sweden,* in nearly the same terms here used. 



The distribution of the till in this state and in eastern Massachusetts 

 is quite irregular. Sometimes no considerable accumulations of it are 

 seen for several miles, and the ledges lie at or near the surface. Else- 

 where the till occurs in large amount, covering the ledges which are 

 scarcely exposed over some whole townships near the coast. Wherever 

 it is found plentifully, it is to a large extent massed in peculiar oblong or 

 sometimes nearly round hills, which usually have quite steep sides and 

 gently sloping, rounded tops, presenting a very smooth and regular con- 

 tour. These hills are of all sizes up to one third or one half mile long, 

 with two thirds as great width ; and their longest axis is most frequently 

 north-west to south-cast, coinciding nearly with the current of the ice- 

 sheet. Their height varies from forty or fifty to two hundred feet. These 

 accumulations of till arc most abundant near the coast, where they some- 

 times occupy nearly the whole territory for many miles, while adjoining 



* Proceediiigs of American Association for the Advancement of Science, vol. 25, 1876. 



