DESICCATION OF THE ASIATIC CONTINENT. 121 



Section III. — Desiccation of the Asiatic Continent, and of other Portions of 



the World. 



Having given an account, in the preceding section, of the phenomena of 

 desiccation in the region of the Cordilleras, it might seem but natural that 

 tlie eastern side of the North American Continent should next be taken up, 

 and considered from the same point of view. But when we come to exam- 

 ine the geological conditions exhibiting themselves in the region east of the 

 Mississippi, and in the vicinity of the Great Lakes, we find that we have to 

 deal with quite a different set of phenomena from those presented on the 

 western side of the continent, and that these introduce new complications 

 into the question of desiccation, rendering the understanding of the prob- 

 lems involved considerably more difficult than we have found to be the case 

 in the discussion of the decrease of the water-surface in the Cordilleras. 

 For this reason it seems best to defer the consideration of the geological 

 facts indicating desiccation in Eastern and Northeastern America until an- 

 other chapter, when they will be taken up in connection with a discussion 

 of some of the general principles involved in desiccation and glaciation. 

 For the present it will be more satisfactory to pursue our review of the phe- 

 nomena indicating decrease of precipitation in a region more closely allied 

 in character with that which forms the subject of the preceding section than 

 is the eastern side of our own continent. 



The poi'tion of the earth's surface to which we now turn is the Asiatic 

 Continent ; and here we find ourselves in the j^resence of conditions ex- 

 tremely similar in character to those which have been described as mani- 

 festing themselves in the Cordilleras ; but on a grander scale, and also 

 vastly more important in their relations to the past history, if not to the 

 future welfare, of mankind. It will become evident, from the facts presented 

 in this section, that Asia has been the scene of great physical changes during 

 the most recent geological times ; that of these no inconsiderable portion 

 has taken place within the historic period ; and that — as there is good rea- 

 son to believe — the development and migrations of great nations have been 

 most powerfully influenced by these changes. 



In the entire continental mass of Europe-Asia (Eurasia, as it is sometimes 

 and very conveniently called, the separation between the two divisions being 

 a purely artificial one) we have, in round numbers, twenty-one million 



