PLEISTOCENE OF EUROPE, NORTH AFRICA, AND NORTH AMERICA 373 



the repeated rise and fall of temperature. Man, first with his crude im- 

 plements and then with his skeletal remains, enters amidst these extinct 

 floras and faunas, and affords a new and very precise means of marking 

 off the stages of geologic time. 



Geographic changes. — Elevation, subsidence, reelevation, is the se- 

 quence of Pleistocene geographic change. The beginning of the Pleisto- 

 cene is remarkal)le for its broad land connections, and represents the last 

 stage of that coimnunity of fauna which during Pliocene times distin- 



PLEISTOCENE 



Fig. 172. — Pleistocene, or Ice Age. A period of maximum total elevation facilitating free 

 migrations and invasions of life, culminating in the Glacial epoch, and followed by a prolonged 

 depression. Portions of northern Europe and the coasts of North America greatly depressed. 

 Then a period of reelevation. Rearranged after W. D. Matthew, 1908. 



guished the entire region of Europe, Asia, and Africa. The central geo- 

 graphic feature of the Ice Age was the continental elevation, which increased 

 the land areas and connections and shut off the warm ocean currents, 

 serving to lower the temperature. During the second Intcrglacial Period 

 there occurred extensive volcanic disturbances in central Europe, giving 

 rise to the hot spring formations of Thuringia (Taubaeh, AVeimar). 



The general and local subsidence which was the chief feature of closing 

 Pleistocene times served to cut off all the old continental connections which 

 had been characteristic of the Tertiary. As to the sequence of this de- 

 pression, Ireland first lost its land connection with Wales and then with 

 Scotland, and Great Britain became faunally isolated. In the Mediter- 

 ranean in mid-Pleistocene times (Pohlig) the land bridge across Gibraltar 



