PERU. 591 
rocks of the island. This stratified bank differs much from the irre- 
gular bed before described. 
The collections of shells with tiles and pottery over the plain south 
of Callao, as well as the beds eighty or eighty-five feet above the sea, 
on San Lorenzo, have been adduced as proofs of an elevation of this 
part of the South American coast. This argument is urged with 
force and discrimination by Mr. Darwin in his Geological work on 
South America. My own observations have been confined to so 
small a part of the coast, that any opinion here expressed is entitled 
to but little weight, especially as lam unable to draw comparisons 
with the beds in other portions of the western coast alleged as simi- 
lar in character. I may, however, frankly confess that the evidence 
does not seem to me to place the question beyond doubt. 
The following are the sources of doubt which have occurred to me 
from the examinations I have made. 
1. ‘The occurrence of the San Lorenzo shells in an irregular bed, 
spread out just beneath the soil or in it, and not at all stratified. 
The action of the ebbing and flowing sea upon a sandy shore, 
arranges the material to some extent in layers, often of extreme deli- 
cacy when the material is fine. A section of any sea-beach proves 
this to be a general fact. And when the material is coarse, a ten- 
dency at least to regularity is apparent. But on San Lorenzo, we find 
none of this kind of evidence to prove that the land at the present 
height of eighty or eighty-five feet was for a time a sea-beach within 
the recent period supposed. ‘The arrangement of the shells affords 
no proof in favour of such an hypothesis, neither does the position 
of any sands, pebbles, or stones in the vicinity. ‘The hypothesis 
that the land was undergoing a slow elevation, would not alter the 
case. Moreover, the view of Mr. Darwin implies (perhaps, however, 
it may not necessarily require) that the shell-bed level was the sea- 
shore for a period of time previous to the elevation, and not merely 
during a rise of the land. 
2. The absence of an inner cliff on San Lorenzo. 
Some traces of two or three terraces have been said to exist around 
San Lorenzo. I observed nothing that I could confidently refer to 
as of this kind. There is an appearance of terraces; but it is slight, 
and may be attributable with more reason to an occasional harder 
layer in the sandstone rocks, which causes it to stand out and give 
protection to others below for some distance, while those above were 
