TERTIARY FORMATION— CHALK. 63 



the great rivers, alternating with sand banks, the clay 

 and loess formations caused by the removal of the soil 

 by the drainage of the glaciers and the floods of running 

 water, which at one time increased periodically to a de- 

 gree truly colossal. The diluvial period, as it seems, in- 

 cludes, both in Europe and America, a repeated glacifica- 

 tion of countries and vast portions of the world, of which 

 the present state of Greenland may now give some idea. 



The period of the series of strata, comprised under 

 the name of the tertiary formation, may be regarded 

 as that during which, at least, the skeleton of the pres- 

 ent continents finally attained its integral configuration. 

 Within its limits fall the erection and upheaval of the 

 great mountain chains, the Cordilleras, Alps, Himalayas, 

 and others; the outlines of the continents were, mean- 

 while, in constant movement. This phenomenon, how- 

 ever, persists throughout all formations, and, as the geo- 

 logical characteristic of the tertiary formation, more stress 

 should be laid on the separation of the earth's surface 

 into climatic zones, approximating to the zones of the 

 present age. The names of the subdivisions are intended 

 to indicate the relation of the animals then living to those 

 of our world, as it was supposed that in the eocene the first 

 animals identical with present species were to be found, 

 more in the miocene, and, yet more, in the pliocene. 



To the chalk formation belong rocks of very various 

 kinds, which can be reduced to one great geological 

 period by means of their contents. If the quartzose 

 sandstone of Saxon Switzerland represents this forma- 

 tion in the centre of Germany, it is from the white chalk 

 of England and Northern France that it took its name. 

 In America, the sandstone has been in a great measure 



