218 DISCUSSION OF THE DESICCATION QUESTION. 



An agency of this character has ah'eady been indicated in the preceding 

 section, namely, an increase of temperature, and it will be proper to take up 

 next this branch of the inquiry, and endeavor to make out whether, in addition 

 to the evidence of a former higher temperature afforded by the phenomena 

 of desiccation, we can produce other and more positive proofs of a change of 

 this character having taken place. It is true that we have in the orographic 

 development of the continental masses an effective cause of a diminution of 

 the rain-fall ; but we are not at liberty to take it for granted that this has 

 been the only one, unless we can prove that all the phenomena of desiccation 

 can be accounted for by orographic changes alone. 



This, however, does not appear to be the case. The drying-up of the 

 continents described in the earlier sections of this chapter seems clearly to 

 present features which cannot be explained on the simple assiunption of an 

 increase of area in the adjacent land masses. This, as the writer believes, 

 cannot but be apparent to the candid in([uirer, who will carefully take into 

 consideration the various facts pre\iously presented, especially when it is 

 remembered that the evidence here laid before the reader forms but a small 

 part of that which might have been furnished, had space permitted. The 

 decrease of the water surface in such cases as that of the Aralo-Caspian 

 Basin or Great Salt Lake is of a character which cannot be fully accounted 

 for by orographic causes alone ; and the same may be said of several of the 

 other regions where similar phenomena have been shown to be taking place. 

 The gradual diminution of the moisture, as well as the shrinking of the water 

 surfaces in general, seems .abundantly proved in regions where it is hardly 

 possible to admit that any orographic changes are going on. To use a 

 homely illustration : there are regions where we can see that the kettle has 

 been more or less completely emptied by having been upset ; in a few cases 

 we may perhaps admit that a crack in its side has let the water run out ; 

 but there are more instances in which the marks indicate clearly enough that 

 the work has been done without violence, and that the kettle has been de- 

 prived of its contents by simple evaporation. 



In view of what has here been stated, it appears that, if not compelled to 

 look for other causes than orographic ones to account for the phenomena of 

 desiccation, we are at least justified in doing so; and since it has been shown 

 that a diminution of the solar radiation, or in other words a decrease of tem- 

 perature on the earth's surface, would certainly be such a valid cause, we are 

 naturally led to inquire whether any proofs, aside from such as have already 



