[835.] DECOMPOSING SHELLS. 369 



There is also another and very difterent class of ruins, which 

 possesses some interest, namely, those of old Callao, overwhelmed 

 by the p^rcat earthquake of 1746, and its accompanying wave. 

 The destruction must have been more complete even than at 

 Talcahuano. Quantities of shingle almost conceal the founda- 

 tions of tiie 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 subsided durins: 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 under- 

 gone 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 con- 

 clusion, 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 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 

 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 sulphate of lime (both probably left 

 by the evaporation of the spray, as the land slowdy rose), to- 

 gether with sulphate of soda and muriate of lime. They rest 

 on fragments of the underlying sandstone, and are covered by a 

 ff^w inches thick of detritus. The shells, higher up on this ter- 

 race, 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 sindlar 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 

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



