68 GRAND CANON DISTEIOT. 



We have also reason to believe that the climate of the Miocene was 

 moist and subtropical, conditions favorable under the circumstances to 

 a rapid rate of erosion. We do not indeed find the proof of this in the 

 province itself, for it contains no Miocene strata or fossils; but in sur- 

 rounding regions the strata and fossils of that age are found in abun- 

 dance, and they clearly indicate that the climate had that character ; and 

 it would be quite untenable to suppose that so limited a tract as the Pla 

 teau Province was an anomaly in respect to the climate of the broader 

 regions of which it is a part, unless special reasous for it could be ad- 

 duced. I know of no such special reasons. But near the close of the 

 Miocene, or not long thereafter, the climate of almost the entire West 

 underwent a change, becoming arid, as it is at present. In this change 

 the Plateau country no doubt shared. The more important results of 

 the Pliocene and Quaternary erosion, however, will be among the prin- 

 cipal themes of the following chapters. 



