220 DISCUSSION OF THE DESICCATION QUESTION. 



having taken place in past ages, before the historic period, can only be proved 

 to haA'e occurred by means of geological evidence.* As so defined, the sub- 

 ject of geological climates is one which has been prominently up for discus- 

 sion, especially during the past few yeans. Hardly a week passes that does 

 not add something to the already voluminous literature of this and allied 

 questions. As already explained, however, the subject of desiccation has in 

 the cour.se of these discussions and investigations been very unsatisfactorily 

 treated, having been left out of consideration altogether, or looked upon as 

 merely a phase of the Glacial epoch. Almost all investigators of geological 

 climates have contented themselves with endeavorina: to show how the 

 "great ice-age" might have been brought about, not only ignoring the 

 local character of this phenomenon, but paying little or no attention to other 

 lines of inquiry, the following of which might have led them to recognize the 

 fact that they were looking at the subject from a very unsatisfactory stand- 

 point. 



It i.s true, however, that, in spite of the fact stated above, namely, that 

 theories of climatic change have almost invariably proved to be simply 

 theories of the Glacial epoch, there has been considerable discussion in the 

 course of which the subject of geological climates has been handled with- 

 out assuming that the only important climatic change which the earth has 

 witnessed has been that in which the great ice-sheet made its appearance. 

 Indeed, there is hardly any possible or conceivable theory or combination 

 of theories which has not been brought forward and upheld by some one, 

 and had there been any satisfactory degree of harmony among those investi- 

 gators who have endeavored to grapple with the entire subject of climatic 

 change, the present writer would not have thought it necessary to add his 

 voice to the discussion. He would not have done so, had he not hoped that 

 he might perhaps apply some of these theories in a manner not hitherto 

 attempted, and, while endeavoring to give due prominence to all the im- 

 portant facts, succeed in bringing the various phases of climatic change into 

 some kind of satisfactory relation to each other. 



It will be assumed that the facts set forth in the preceding pages in regard 

 to the desiccation do render it, if not certain, at least probable that other 



* This definition is not intended to exclude tlie seeking of assistance from other branches of science in the 

 prosecution of an imiuiry into the climatic changes of past geological times. Whatever light might, for instance, 

 be thrown upon the subject by astronomy would of course be welcomed, and it is from that source especially that 

 possible information as to the causes of any such indicated changes would be expected. 



