GLACIAL FORMATIONS IN NORTH AMERICx\. 183 
lines of equal winter temperature. It seems that formerly, 
as now, a more extreme climate and a more abundant sup¬ 
ply of ice prevailed on the western side of the Atlantic. An¬ 
other resemblance between the distribution of the drift fos¬ 
sils in Europe and North America has yet to be pointed out. 
In Canada and the United States, as in Europe, the marine 
shells are generally confined to very moderate elevations 
above the sea (between 100 and 700 feet), while the erratic 
blocks and the grooved and polished surfaces of rock extend 
to elevations of several thousand feet. 
I have already mentioned that in Europe several quadru¬ 
peds of living, as well as extinct, species were common to 
pre-glacial and post-glacial times. In like manner there is 
reason to suppose that in North America much, of the an¬ 
cient mammalian fauna, together with nearly all the inverte- 
brata, lived through the ages of intense cold. That in the 
United States the Mastodon giganteus was very abundant 
after the drift period, is evident from the fact that entire 
skeletons of this animal are met with in bogs and lacustrine 
deposits occupying hollows in the glacial drift. They some¬ 
times occur in the bottom even of small ponds recently 
drained bv the agriculturist for the sake of the shell-marl. 
In 1845 no less than six skeletons of the same species of 
Mastodon were found in Warren county. New Jersey, six 
feet below the surface, by a farmer who was digging out the 
rich mud from a small pond which he had drained. Five 
of these skeletons were lying together, and a large part of 
the bones crumbled to pieces as soon as they were exposed 
to the air. 
It would be rash, however, to infer from such data that 
these quadrupeds were mired in modern times, unless we 
use that term strictly in a geological sense. I have shown 
that there is a fluviatile deposit in the valley of the Niagara, 
containing shells of the genera Melania^ Lymnea^ PlanorMs^ 
Valvata^ Cydaz^ Tlnio^ Ilelix^ etc., all of recent species, from 
which the bones of the great Mastodon have been taken in 
a very perfect state. Yet the whole excavation of the ra¬ 
vine, for many miles below the Falls, has been slowly effect¬ 
ed since that fluviatile deposit was thrown down. Other 
extinct animals accompany the Mastodon giganteus in the 
post-glacial deposits of the United States, and this, taken 
with the fact that so few of the mollusca, even of the com¬ 
mencement of the cold period, differ from species now living 
is important, as refuting the hypothesis, for which some have 
contended, that the intensity of the glacial cold annihilated 
all the species in temperate and arctic latitudes. 
