THE FORMATION OF TERRACES. 73 



the formation of these great natural terraces can be 

 accounted for, we humbly venture to suggest that we 

 see in those slopes the probable results of subsidence, 

 when the land was still in a soft condition, such as 

 that of clay or mud ; as distinguished from its probably 

 more or less hardened condition when it cracked away, 

 leaving the lines of towering bluffs upstanding, of which 

 we have already spoken ; beyond that we think it would 

 hardly be expedient at present to attempt to carry 

 this question. 



There are many examples of these great elevated 

 table-lands in Nature, notably in Peru and Bolivia, in 

 South America, but above all in Thibet, where the 

 average level of the table-land may be taken as about 

 15,000 feet above sea-level. * This magnificent plateau 

 is bounded by some of the loftiest known peaks in the 

 world, many of them exceeding 20,000 feet in height, 

 while the dimension of the Thibetan mountain area, 

 from east to west, is about 2000 miles, and its average 

 breadth somewhat over 500 miles, f 



Let the reader imagine, if he can, the gigantic nature 

 of the forces which have upheaved this immense region 

 to these altitudes for mountain chains are created by 

 upheavals, as we shall show in due course. Hardly 

 inferior, however, either in extent or in elevation, are 

 the table-lands in the interior of Peru, ranging from 

 1 1 ,000 to 1 4,000 feet above sea-level, and bordered 

 by the great range of the Cordilleras. The famous 

 saline lake of Titicaca, almost equalling Ontario in 

 extent, is here found embedded in the hills, at a height 



* Encycl. Brit. Vol. xi, Qth edit., p. 822. 

 I Ibid., p. 822. 



