OSBORN, REVIEW OF THE PLEISTOCENE 239 



SUBSIDENCE, submergence of the laud aud advance of the sea, land con- 

 nections interrupted, advance of the glaciers, periods of deposition and 

 filling of the valleys. 



Thus Boule and Geikie consider the glacial stages as mainly periods of 

 continental subsidence and filling of the valleys, the interglacial as times 

 of elevation and erosion of valleys and terraces. Penek estimates the 

 elevation of southern Europe at 100m. in the beginning of Pleistocene 

 times; he speaks of the elevation of the Alps during the Second Inter- 

 glacial Stage. Geikie describes the southern half of the North Sea as 

 dry land during the First Interglacial Stage traversed by a northern ex- 

 tension of the Eiver Rhine, while the approach of the Second Glacial 

 Stage was heralded by a submergence of this area of the North Sea. 

 Again (Geikie) during the Second Interglacial Stage the English Chan- 

 nel and probably a large part of the North Sea became dry land. Finally 

 (Pohlig) during the Third Interglacial Stage there was a period of 

 continental elevation and a dry, cold steppe climate in western Europe. 



Consistent with this hypothesis is the deposition of loess during the 

 Second and Third Interglacial Stages, also during the Postglacial Stage, 

 because loess deposition is characteristic of dry and elevated continental 

 climates with winds prevailing in one direction. 



Final Subsidence. — Consistent with this hypothesis also is the fact tbat 

 general and local subsidence in the northern hemisphere was the chief 

 feature of closing Pleistocene times or the very cold Postglacial Stage; 

 all the old continental connections which had been characteristic of the 

 Tertiary were cut off; in the northwest the English Channel was formed, 

 Great Britain became isolated from Europe, Ireland first lost its land 

 connection with Wales and then with Scotland ; to the eastward the Medi- 

 terranean Sea extended into the .ZEgean region and cut off the old land 

 connection between Greece and Asia, which had so long served to connect 

 Greece with the mammalian life of southern Asia. During a period of 

 extreme subsidence, the Black Sea, the Caspian, the Sea of Aral formed 

 a large single sheet of water known as the Hyrcanian Sea. In southern 

 Asia similar subsidence and separation phenomena were in progress; the 

 islands of the East Indies, Sumatra and Java were cut off from the 

 Malay Peninsula. The separation of the Japan and Philippine archi- 

 pelagos probably occurred in late Postglacial times. To the far north- 

 east late in Pleistocene times Asia lost its connection with America, 

 Bering Straits were reopened, and the so-called Nearctic region of North 

 America was completely isolated from the Palsearctic region of Eurasia 

 after a long period of community and free intermigration of Holarctic 

 life. 



