TO 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 Tz//. 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-east, coinciding nearly with the current of the ice- 
sheet. Their height varies from forty or fifty to two hundred feet. These 
accumulations of till are most abundant near the coast, where they some- 
times occupy nearly the whole territory for many miles, while adjoining 
* Proceedings of American A iation for the Ad: t of Science, vol. 25, 1876. 
