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 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), 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
trace of organic structure.
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