CHAP. IX,] 



ANCIF]NT 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 daring 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 v^^ithout 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 



