I913-] SEE— ORIGIN OF HIMALAYA MOUNTAINS. 501 



of the plateau probably is in Colorado, where the whole Pacific 

 plateau is widest ; but this only indicates that the forces which raised 

 such high mountains as Pike's Peak also raised a high plateau in 

 the general region, independent of the width of the plateau after- 

 wards elevated from the sea. And so on generally. 



The rule that the plateau decreases in height when it increases in 

 width, must be understood to apply to a region of not too great 

 width. For when the width is very great, we have rather a series of 

 plateaus added together side by side than a single one ; and the final 

 result is a composite efifect, one plateau section fitting onto another, 

 and the whole series of sections running together as an unbroken 

 embankment of variable height. 



In view of these considerations, a plateau so wide as that between 

 Colorado and California is really a series of plateaus, each of 

 unusual width at this point, and the whole effect therefore a very 

 broad compound plateau. The entire Pacific Plateau is the cumula- 

 tive work of the ocean, done in successive sections ; and as the ocean 

 is deepest opposite California, the uplift naturally has been greatest 

 in this part, which also developed the Sierra Nevada Mountains, 

 and at a still earlier stage the Wasatch range in Utah. 



The history of the building of the Pacific plateau from Colorado 

 to California is too long to be described here, but these hints on 

 the method by which it was elevated give some idea of the growth 

 of the continent westward from' the ancient border which was east 

 of the present Rocky Mountain range. 



4. The Cause of the Great Height of the Plateaus of 

 Western Tibet and Titicaca. 



Since writing the memoirs of 1906-08, I have had occasion to 

 reexamine the relationships of the great mountains to the plateaus, 

 and of the plateaus to the sea, with the result of confirming in the 

 most conclusive manner the uplift of the plateaus by the ocean. It 

 is found that the plateau of western Tibet has almost exactly the 

 relationship to the ancient sea valley formerly covering northern 

 India, that the plateau of Titicaca now has to the border of the 

 Pacific Ocean. 



