134 PERU. 



no people in their senses would willingly have 

 chosen for their building-place the narrow spit of 

 shingle on which the ruins now stand. Since our 

 voyage, M. Tschudi has come to the conclusion, 

 by the comparison of old and modern maps, that 

 the coast both north and south of Lima has cer- 

 tainly subsided. 



On the island of San Lorenzo, there are very 

 satisfactory proofs of elevation within the recent 

 period ; this, of course, is not opposed to the belief 

 of a small sinking of the ground having subse- 

 quently taken place. The side of this island front- 

 ing the Bay of Callao is worn into three obscure 

 terraces, the lower one of which is covered by a 

 bed a mile in length, almost wholly composed of 

 shells of eighteen species, now living in the adjoin- 

 ing sea. The height of this bed is eighty-five feet. 

 Many of the shells are deeply corroded, and have 

 a much older and more decayed appearance than 

 those at the height of 500 or 600 feet on the coast 

 of Chile. These shells are associated with much 

 common salt, a little sulphate of lime (both proba- 

 bly left by the evaporation of the spray, as the 

 land slowly rose), together with sulphate of soda 

 and muriate of lime. They rest on fragments of 

 the underlying sandstone, and are covered by a 

 few inches thick of detritus. The shells, higher 

 up on this terrace, could be traced scaling off in 

 flakes, and falling into an impalpable powder ; and 

 on an upper terrace, at the height of 170 feet, and 

 likewise at some considerably higher points, I 

 found a layer of saline powder of exactly similar 

 appearance, and lying in the same relative posi- 

 tion. I have no doubt that this upper layer origi- 

 nally existed as a bed of shells, like that on the 

 eighty-five-feet ledge ; but it does not now contain 

 even a trace of organic structure. The powder 



