GEOLOGY AND GEO-BOTANY OF ASIA. 69 



What arc now the lowlands of Asia must have been widely sub- 

 merged by the seas of the Tertiary period, as also those of the Quater- 

 nary (Post-Pliocene) period. During this last period, the whole of 

 the lowlands of northwest Siberia were under the sea, as far as the 

 fiftieth degree of latitude, a broad gulf of the Arctic Ocean penetratiug 

 at the eastern foot of the Urals as far as the watershed which now 

 separates the basin of the Obi from the Aral-Caspian Sea. At the 

 same time there are no traces of that sea on the high plains of east 

 Siberia, which were only intersected by several narrow elongated gulfs 

 of the ocean. The moistness that thus ensued permitted glaciers 

 (which are wanting now throughout the middle parts of east Siberia 

 and Mongolia) freely to accumulate, so that the whole of the upper 

 plateau and its border-ridges were under a mighty ice-cap. Immense 

 glaciers, like those of the Alps and Jura, covered also the alpine re- 

 gions. How far glaciation extended over the plateau of Tibet and in 

 China still remains unsettled. In Turkestan and Siberia immense 

 accumulations of loess fringe the alpine regions; while in China they 

 cover immense tracts, and are the most fertile regions of Asia. 



Many important changes in the distribution of land and water have 

 been going on in Asia since the Glacial period, and even during his- 

 torical times. Since the Aral- Caspian Sea became isolated from the 

 ocean, its desiccation, as well as that of the numberless lakes which 

 dotted the surface of Asia during the Lacustrine (Post-Glacial) period, 

 has proceeded with a rapidity which may be guessed from the very 

 rapid rate at which the process has been observed to go on in Siberia 

 during the last hundred years. All Asia bears unmistakable traces 

 of having been covered during the Lacustrine period with numberless 

 large and small lakes, which have now disappeared, not in consequence 

 of the action of man, but in consequence of some general causes affect- 

 ing the earth's surface since the last Glacial period. The process is 

 still more accelerated by the rapid upheaval of the continent — the 

 whole of the Arctic coast, as also most of that washed by the Pacific, 

 the Mediterranean, the Eed Sea and parts of the Indian Ocean, being 

 in a state of gradual elevation, while the few areas where traces of 

 subsidence have been noticed are very limited. The influence of the 

 desiccation of Asia has been felt even during historical times, and the 

 migrations of the Ural- Altaians, Turks and Mongols will probably be 

 best explained if this change in the condition of central Asia be taken 

 into account; while the same circumstance explains the present nearly 

 desert state of those regions which were the cradle of European civil- 

 ization. 



Volcanoes play an important part in Asia's geology; no less than 

 122 active volcanoes are already known in Asia, chiefly in the islands 

 of southeast Asia, the Philippines, Japan, the Kuriles and Kamchatka, 



