The Shoshone Island. 93 



ive shore lines were worked by the same 

 ocean, receiving into their deposits the re- 

 mains of the same sea life, and were affected 

 alike by the heat and pressure of their vast 

 accumulations of the wear and the wash of 

 older things. Nothing of all this tended to 

 make these islands unlike, and so their growth 

 was treated as the growth of twin sisters. The 

 divergence in their records commenced with 

 the growth of the Cascade barrier between 

 them, and of the early history of this and its 

 special bearing on the development of the 

 Shoshone island, careful note has been at- 

 tempted. 



At a later period in its history, this barrier 

 character took another form. From a mere 

 water barrier to a range of hills, and still later 

 to a vast range of mountains, increased eleva- 

 tion lifted it into an atmospheric agency quite 

 as important as its previous marine one, for 

 when it reached the altitude of a mountain 

 range it excluded the moist, warm current 

 of the Pacific ocean and thus surrendered the 



