206 



PATAGONIA. 



Jan. 1834. 



there is not a single point of eruption; yet in former ages^ 

 as we shall hereafter show, deluges of lava flowed from that 

 very part. It is in conformity with our hypothesis that this 

 southern region of repose, is at present suffering from the 

 inroads of the ocean, as attested by the long line of cliff on 

 the Patagonian coast. Such we believe to have been the 

 causes of this singular configuration of the land. Neverthe- 

 less, we confess that it at first appears startling, that the 

 most marked intervals between the heights of the successive 

 plains should, instead of some great and sudden action of the 

 subterranean forces, only indicate a longer period of repose. 



In explaining the widely-spread bed of gravel, we must first 

 suppose a great mass of shingle to be collected by the action 

 of innumerable torrents, and the swell of an open ocean, 

 at the submarine basis of the Andes, prior to the elevation of 

 the plains of Patagonia. If such a mass should then be 

 lifted up, and left exposed during one of the periods of 

 subterranean repose ; a certain breadth, for instance a mile, 

 would be washed down, and spread out over the bottom of 

 the invading waters. (That the sea near the coast can carry 

 out pebbles, we may feel sure from the circumstance of 

 their gradual decrease in size, according to the distance from 

 the coast-line.) 



If this part of the sea should now be elevated, we should 

 have a bed of gravel, but it would be of less thickness than 

 in the first mass, both because it is spread over a larger area, 

 and because it has been much reduced by attrition. This pro- 

 cess being repeated, we might carry beds of gravel, always 

 decreasing in thickness (as happens in Patagonia) to a con- 

 siderable distance from the line of parent rock.* For instance, 

 on the banks of the St. Cruz at the distance of one hundred ^ 



* It is needless to point out to the geologist, that this view, if correct, 

 will account, without the necessity of any sudden rush of water, for the 

 general covering of mixed shingle, so common in many parts of Europe, 

 and likewise for the occurrence of widely-extended strata of conglomerate ; 

 for the superficial beds might, during a period of subsidence, be covered by 

 fresh deposits. 



