170 DISCUSSION OF THE DESICCATION QUESTION. 



quence of their extermination by man the climate of those regions has be- 

 come cold, inhospitable, and unfavorable to arboreal growth, as we now find 

 it to be. No more can it be assumed as jmma facie true, that any part of the 

 earth's surface, if now destitute of trees, has been rendered so by the hand 

 of man. Evidence, clear and convincing to that effect, must be furnished, be- 

 fore credence can be given to statements of this kind. More than this, if 

 it can be shown that the trees which formerly covered any given area have 

 been cut down, and that the climate in such a locality, once fiivorable, hns 

 now become of a character hostile to the prosperity and intellectual develop- 

 ment of man, it remains still to be proved that it is the removal of the 

 forests which has been the effective agent in bringing about this changed 

 condition of things. 



If it bo true that the desiccation of certain regions, which seem on trust- 

 worthy evidence, as set forth in the preceding pages, to have become drier 

 during the historic period, was begun long before man could have been in 

 existence to interfere with nature's work, then we shall have strong reason 

 to infer that Avhat was begun Avithout the interference of man, and continued 

 for an indefinite period without it, may be still going on in the same way, 

 and that we are only the witnesses of the continuous working of an agency 

 which would have remained effective even if the earth had never become 

 inhabited by man or animal. 



That the drying-up of the Central Asiatic and the Cordilleran regions is a 

 phenomenon Aviiich was begun long before man could have interfered with 

 the course of nature, seems evident from the facts which have been set forth 

 in the preceding chapter. Whether we consider the diminution of the Ter- 

 tiary rivers of California to their present comparatively insignificant size, 

 the dwindling away of the lacustrine areas of the Great Basin, or the similar 

 condition of things shown to have been begun in the heart of the Asiatic 

 Continent at least as early as the Tertiary period, we are forced to admit 

 that we have to do with a phenomenon as far beyond man in the length of 

 time it has been in operation as it is beyond the scope of his powers from 

 the point of view of its magnitude. 



No one has ever suggested that the drying-up of the region of the 

 Cordilleras was due to the action of man ; neither has a similar claim been 

 urged, to any considerable extent, with regard to the vast area of Central 

 Asia where the phenomena of desiccation present themselves in such a strik- 

 ing manner. Neither has it been suggested with reference to the great 



