Jan. 1834. 



GEOLOGY. 



205 



the consequence of the shoaling bed of an ocean, elevated at 

 a perfectly equal)le rate, so that the same number of feet 

 should be converted into dry land in each succeeding century. 

 Every part of the surface would then have been exposed for 

 an equal length of time to the action of the beach-Hne, and 

 the whole in consequence equally modified. The shoaling bed 

 of the ocean would thus be changed into a sloping land, with 

 no marked line on it. If, however, there should occur a long 

 period of repose in the elevations, and the currents of the 

 sea should tend to wear away the land (as happens along this 

 whole coast), then there would be formed a line of cliff. 

 Accordingly as the repose was long, so would be the quan- 

 tity of land consumed, and the consequent height of such 

 cliffs. Let the elevations recommence, and another sloping 

 bank (of shingle, or sand, or mud, according to the nature of 

 the successive beach-lines) must be formed, which again will 

 be broken by as many lines of cliff, as there shall be periods 

 of rest in the action of the subterranean forces. Now this is 

 the structure of the plains of Patagonia ; and such gradual 

 changes harmonize well with the undisturbed strata, extend- 

 ing over so many hundred miles. 



I must here observe, that I am far from supposing that 

 the entire coast of this part of the continent has ever been 

 lifted up, to the height of even a foot, at any one moment of 

 time ; but, drawing our analogies from the shores of the 

 Pacific, that the whole may have been insensibly rising, with 

 every now and then a paroxysmal or accelerated movement 

 in certain spots. With respect to the alternation of the 

 periods of such continued rise and those of quiescence, we 

 may grant that they are probable, because such alternation 

 agrees with what we see in the action, not only of a single 

 volcano, but likewise of the disturbances affecting whole 

 regions of the earth. At the present day, to the north of the 

 parallel 44°, the subterranean forces are constantly manifest- 

 ing their power over a space of more than one thousand 

 miles. But to the southward of that line, as far as Cape 

 Horn, an earthquake is seldom or never experienced, and 



