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:
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