The Powder Has Been Analyzed
For Me By Mr. T. Reeks; It Consists Of Sulphates And Muriates
Both Of Lime And Soda, With Very Little Carbonate Of
Lime.
It is known that common salt and carbonate of lime
left in a mass for some time together, partly decompose each
other; though this does not happen with small quantities in
solution.
As the half-decomposed shells in the lower parts
are associated with much common salt, together with some
of the saline substances composing the upper saline layer,
and as these shells are corroded and decayed in a remarkable
manner, I strongly suspect that this double decomposition
has here taken place. The resultant salts, however, ought
to be carbonate of soda and muriate of lime, the latter is
present, but not the carbonate of soda. Hence I am led to
imagine that by some unexplained means, the carbonate of
soda becomes changed into the sulphate. It is obvious that
the saline layer could not have been preserved in any country
in which abundant rain occasionally fell: on the other
hand, this very circumstance, which at first sight appears so
highly favourable to the long preservation of exposed shells,
has probably been the indirect means, through the common
salt not having been washed away, of their decomposition
and early decay.
I was much interested by finding on the terrace, at the
height of eighty-five feet, _embedded_ amidst the shells and
much sea-drifted rubbish, some bits of cotton thread, plaited
rush, and the head of a stalk of Indian corn: I compared
these relics with similar ones taken out of the Huacas, or old
Peruvian tombs, and found them identical in appearance.
On the mainland in front of San Lorenzo, near Bellavista,
there is an extensive and level plain about a hundred feet
high, of which the lower part is formed of alternating layers
of sand and impure clay, together with some gravel, and the
surface, to the depth of from three to six feet, of a reddish
loam, containing a few scattered sea-shells and numerous
small fragments of coarse red earthenware, more abundant
at certain spots than at others. At first I was inclined to
believe that this superficial bed, from its wide extent and
smoothness, must have been deposited beneath the sea; but
I afterwards found in one spot, that it lay on an artificial
floor of round stones. It seems, therefore, most probable
that at a period when the land stood at a lower level there
was a plain very similar to that now surrounding Callao,
which being protected by a shingle beach, is raised but very
little above the level of the sea. On this plain, with its
underlying red-clay beds, I imagine that the Indians
manufactured their earthen vessels; and that, during some
violent earthquake, the sea broke over the beach, and converted
the plain into a temporary lake, as happened round Callao in
1713 and 1746. The water would then have deposited mud,
containing fragments of pottery from the kilns, more abundant
at some spots than at others, and shells from the sea.
This bed, with fossil earthenware, stands at about the
same height with the shells on the lower terrace of San
Lorenzo, in which the cotton-thread and other relics were
embedded.
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