78 
braced in the Drift period, it will be necessary to make a 
brief review of these phenomena so far as they are known to 
us. » | 
The geological periods immediately antecedent to the Drift 
are the Cretaceous, which was a period of marked continental 
submergence, when the ocean covered most of the Western 
half of the continent and reached several hundred feet higher 
than now over the basis, of the eastern highlands; and the 
Tertiary with its three subdivisions Eocene, Miocene and 
Pliocene. The Kocene was a period of continental progress- 
ive emergence—land area gradually expanding, climate sub- 
tropical. In the Miocene and Pliocene epochs the topogra- 
phy was in a general way what it is now, but in detail the sur- 
face was considerably more diversified, especially by the pres- 
ence of great fresh-water lakes which occupied much of the 
surface on both sides of the Rocky Mountains. At this time 
there was probably a land connection between the. northern 
part of North America and Europe on the one hand and 
Asia on the other. The climates of Alaska and Greenland 
were then as mild as that of Virginia now; the flora was 
luxuriant and varied, and was common to Kurope, Iceland, 
Spitzbergen, Greenland, our continent and North-eastern 
Asia; palms grew further north than the Canadian line. 
The fauna was much richer than now, including Hlephant, 
Rhinoceros and many other animals not. now living in either 
of the Americas, and indeed as large a number of the great 
mammals as are now found in Africa. 
This picture which geology gives us of our continent—the 
picture of a country more beautiful and fertile than now, 
covered with a more luxuriant and varied vegetation and 
with a much nobler fauna, is followed by another almost its 
opposite in all things. .This is the Ice period, when the pres- 
ent climate of Greenland was brought down to New York, 
when the continent was several hundred feet higher than 
now and a large part of the surface covered with glaciers as 
far down as the line of the Ohio. This period continued 
long enough to produce a general planing down and grinding 
off of the surface rocks, and long enough for the draining 
