132 



UPHEAVAL AND SUBSIDENCE 



[Ch. VII. 



undeniable, for marine remains are found in rocks at almost 

 all elevations above the sea, and the denudation which the 

 dry land appears to have suffered, favours the idea that it 

 was raised from the deep by a succession of upward move- 

 ments, prolonged throughout indefinite periods. Bain and 

 rivers, aided sometimes by slow and sometimes by sudden 

 and violent movements of the earth's crust, have undoubtedly 

 excavated some of the principal valleys ; but there are al~ - 

 wide spaces which have been denuded in such a manner 

 can only be explained by reference to the action of waves 



so 

 as 



from 



Crossing 



But perhaps it may be said that there is no analogy be- 

 tween the slow upheaval of broad plains or table-lands, and 

 the manner in which we must presume all mountain-chains, 

 with their inclined strata, to have originated. It seems, how- 

 ever, that the Andes have been rising century after century, 

 at the rate of several feet, while the Pampas on the east have 

 been raised only a few inches in the same time, 

 from the Atlantic to the Pacific, in a line passing through 

 Mendoza, Mr. Darwin traversed a plain 800 miles broad, the 

 eastern part of which has emerged from beneath the sea at a 

 very modern period. The slope from the Atlantic is at first 

 very gentle, then greater, until the traveller finds, on reach- 

 ing Mendoza, that he has gained, almost insensibly, a height 

 of 4,000 feet. Th " " 



s mountainous 

 om Mendoza ' 



HI] 



om 



Now 



nent peaks, which ascend much higher. 



to explain the origin of the principal inequalities of level here 



imagine 



ment to the west of Mendoza, and, secondly, to the east oi 

 that place, an upheaving force, which died away gradually 

 as it approached the Atlantic. In short, we are only ca lee 

 upon to conceive, that the region of the Andes was pushect 

 up four feet in the same period in which the Pampas near 



Mendo 



the Atlantic one inch. 



North 



Cape is said to ascend about five feet in a century, wn 





li, 



