6oo Summary of Recent Elevatory paet n. 



parative rest. At several places tlie land has been 

 lately, or still is, rising both insensibly and by sudden 

 starts of a few feet during earthquake-shocks ; this 

 shows that these two kinds of upward movement are 

 intimately connected together. For a space of 775 

 miles, upraised recent shells are found, on the two op- 

 posite sides of the continent ; and in the southern half 

 of this space, it may be safely inferred from the slope 

 of the land up to the Cordillera, and from the shells 

 found in the central part of Tierra del Fuego, and high 

 up the river Santa Cruz, that the entire breadth of the 

 continent has been uplifted. From the general oc- 

 currence on both coasts of successive lines of escarp- 

 ments, of sandunes and marks of erosion, we must 



conclude that the elevatorv movement has been nor- 



1/ 



mally interrupted by periods, when the land either was 

 stationary, or when it rose at so slow a rate as not to 

 resist the average denuding power of the waves, or 

 when it subsided. In the case of the present high sea- 

 cliffs of Patagonia and in other analogous instances, we 

 have seen that the difficulty in understanding how 

 strata can be removed at those depths under the sea, at 

 which the currents and oscillations of the water are 

 depositing a smooth surface of mud, sand, and sifted 

 pebbles, leads to the suspicion that the formation or 

 denudation of such cliffs has been accompanied by a 

 sinking movement. 



In South America, everything has taken place on a 

 grand scale, and all geological phenomena are still in 

 active operation. We know how violent at the present 

 day the earthquakes are, we have seen how great an 

 area is now rising, and the plains of tertiary origin are 

 of vast dimensions ; an almost straight line can be 

 drawn from Tierra del Fuego for 1,600 miles northward, 

 and probably for a much greater distance, which shall 



