382 GREAT MOUNTAIN PLATEAUX. 



parallel ridges seems to have taken place simultaneously, 

 considerable areas of these sedimentary rocks are often 

 found to have been entirely separated from the rest 

 of these strata, and carried up so as to occupy the 

 floors of the valleys or high plateaux which in such 

 cases are generally found to fill the spaces between 

 the ridges. Magnificent examples of these elevated 

 plateaux are to be found in Thibet, where they extend 

 for hundreds of miles, at an altitude averaging say 

 about 16,500 feet above the level of the sea. Other 

 instances, second only to those of Thibet, are to be 

 found in the Peruvian and Bolivian Andes, where vast 

 table lands exist, ranging from 1 1,000 to 14,000 feet 

 above sea level, surrounded by some of the grandest 

 mountain scenery to be found in the world. * 



In the case of adjacent and parallel chains of moun- 

 tains, of which there are such numerous instances, the 

 question will naturally arise was the upheaval of these 

 several chains simultaneous ? or did it occur at differ- 

 ent periods of time? Of course the reply must be to 

 a great extent conjectural; nevertheless, careful 

 scientific observers have come to the conclusion that 

 the balance of probabilities appears to require an affirm- 

 ative answer. In the case of the Alps, a chain of 

 mountains which has been the subject of much more 

 general and careful study than any other, the evidence 

 In support of the hypothesis of simultaneous upheaval 

 seems very strong. 



"The broad fact (says Dr. Ball) that the same sedimen- 

 tary deposits, varying very little in mineral character, extend 



* See paper by Colonel Trotter, R.E., giving an account of the journey 

 of the Pundit Nain Sing in Great Thibet from Leh in Ladakh to Llasa ; 

 in Journal of Royal Geographical Society, Vol. 47, p. 9. 



