498 SEE— ORIGIN OF HIMALAYA MOUNTAINS. [April 18, 



It is noticeable that the height decreases from 12,600 feet near 

 Lake Titicaca, to 11,000 feet in central Peru, and perhaps 10,000 

 feet at Quito ; while south of Titicaca the height does not decrease 

 appreciably till central Chile is reached, after which it falls steadily 

 till the continent sinks beneath the sea at Cape Horn. 



Now it is remarkable that if we take a typical section of the 

 highest and broadest part of the Andean plateau, 2.5 miles high by 

 300 miles wide, the numerical product of width by height in miles 

 is 750. And the Rocky Mountain plateau, i mile high and 750 miles 

 wide, gives the same product, 750 square miles. 



To be sure this product can be varied considerably by taking 

 different sections of the plateaus of North and South America, but 

 all in all this average estimate appears to be a fair one. For in the 

 article " Andes," in the encyclopedia Britannica, 9th edition. Sir 

 Archibald Geikie estimates the bulk of the Andes as of the average 

 width of 100 miles, and height of 13,000 feet. The present estimate 

 gives greater width but somewhat less height. 



On the whole, I am inclined to think that the average sectional 

 volume of the Andes is somewhat less than that in the Rocky Moun- 

 tain plateau ; for between Colorado and the Pacific coast the width 

 is about 1,500 miles, and the average height about a mile. The 

 plateau is much narrower in Canada, and very much narrower in 

 Mexico, practically disappearing entirely in Central America and 

 Panama. Thus at one point in the United States the sectional con- 

 tents may be twice that in the Andes ; yet the average sectional 

 volume for the Pacific plateau of North America is not much 

 greater than the larger sectional volumes for the plateau of the 

 Andes. 



The significance of this equality in the volumes of the two 

 plateaus lies in the fact that both are the product of the common 

 Pacific Ocean, one in the northern, the other in the southern con- 

 tinent. The new theory does not require that the volumes should 

 be exactly equal, but it implies that they should be comparable, and 

 such is the fact in a very striking degree. 



Let us now consider the plateau of Tibet, in comparison with 

 that of the Andes. The height of western Tibet is about 15,000 



