CHAP. IX.] 
ANCIENT GLACIAL EPOCHS. 
171 
was almost exactly the same as it is now, and it continually in- 
creased from that time up to the glacial epoch. Now if we take 
double the present excentricity as being sufficient to produce 
some glaciation in the temperate zone, we find (by drawing out 
the diagram at p. 165 on a larger scale) that during 1,150,000 
years out of the 2,400,000 years immediately preceding the last 
glacial epoch, the excentricity reached or exceeded this amount, 
consisting of sixteen separate epochs, divided from each other by 
periods varying from 30,000 to 200,000 years. But if the last 
glacial epoch was at its maximum 200,000 years ago, a space 
of three million years will certainly include much, if not all, of 
the Tertiary period ; and even if it does not, we have no reason 
to suppose that the character of the excentricity would suddenly 
change beyond the three million years. 
It follows, therefore, that if periods of high excentricity, like 
that which appears to have been synchronous with our last glacial 
epoch and is generally admitted to have been one of its efficient 
causes, always produced glacial epochs (with or without alternat- 
ing warm periods), then the whole of the Tertiary deposits in the 
north temperate and Arctic zones should exhibit constantly 
alternating boulder and rock-bearing beds, or coarse rock-strewn 
gravels analogous to our existing glacial drift, and with some 
corresponding change of organic remains. Let us then see what 
evidence can be adduced of the existence of such deposits, and 
whether it is adequate to support the theory of repeated glacial 
epochs during the Tertiary period. 
Evidences of Ice- action during the Tertiary Period. — The 
Tertiary fossils both of Europe and North America indicate 
throughout warm or temperate climates, except those of the 
more recent Pliocene deposits which merge into the earlier 
glacial beds. The Miocene deposits of Central and Southern 
Europe, for example, contain marine shells of some genera now 
only found farther south, while the fossil plants often resemble 
those of Madeira and the southern states of North America. 
Large reptiles, too, abounded, and man-like apes lived in the south 
of France and in Germany. Yet in Northern Italy, near Turin, 
there are beds of sandstone and conglomerate full of character- 
istic Miocene shells, but containing in an intercalated deposit 
