390 CHARLES DARWIN 



which possesses some interest, namely, those of old Callao. 

 overwhelmed by the great earthquake of 1746, and its ac- 

 companying wave. The destruction must have been more 

 complete even than at Talcahuano. Quantities of shingle 

 almost conceal the foundations of the walls, and vast masses 

 of brickwork appear to have been whirled about like pebbles 

 by the retiring waves. It has been stated that the land sub- 

 sided during this memorable shock: I could not discover any 

 proof of this; yet it seems far from improbable, for the 

 form of the coast must certainly have undergone some change 

 since the foundation of the old town; as 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 certainly 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 subsequently taken place. The side of this island 

 fronting the Bay of Callao, is worn into three obscure ter- 

 races, 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 adjoining 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 sul- 

 phate of lime (both probably 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 position. I have no doubt that this 

 upper layer originally existed as a bed of shells, like that on 

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



