STRATA OF THE TERTIARY FORMATION. 77 



of Switzerland then those periods during which 

 the steppe fauna might have dispersed must have 

 been the intermediate epochs. However, we still 

 require much enlightenment on this point, and much 

 also remains to be explained as regards the causes 

 of all these ice formations. 



It is not known how far back Man extends into 

 the Tertiary period. In the central and northern 

 latitudes of the Old World as well as of America 

 he could, of course, not gather into communities, 

 or rise above his origin, till the Glacial period (as 

 may be assumed) gave way to incalculably long ages 

 of assured order in the later geological period. 

 And Man's distribution over the earth is accom- 

 panied by a diminution of the animals. 



THE STRATA OF THE TERTIARY FORMATION. 



Air-breathing animals are met with first in the 

 Coal formation. Thereupon we have in succession 

 the Dyas formation (in Germany, Kupferschiefer 

 and Eothliegendes), the Trias (bunter Sandstein, 

 Muschelkalk, Keuper), the Jura with its numerous 

 divisions, and the Chalk. We possess a few fossil 

 remains of Mammalia even from the Trias and 

 Jura formations. Nothing is preserved in the 

 Chalk. On the other hand, the subdivisions of the 

 Tertiary are unusually rich in fossil remains of 



