1835.] | DECOMPOSING SHELLS. 3e8 
There is also another and very different class of ruins, which 
possesses some interest, namely, those of old Callao, overwhelmed 
by the great 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 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 subsided 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 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 slowly rose), to- 
gether 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 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 similar appearance, 
and lying in the same relative position. I have no doubt that 
this upper Jayer originally existed as a bed of shells, like that on 
the eighty-five-feet ledge; but it does not now contain even a 
* 
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