322
ON THE NATURAL HISTORY
character to the presence of pyrites : "That these baths or
waters are derived from such, the marcasites which the
Grecians call Pyritis, per antonomasiam (for being smit with the
iron, it yeeldeth more sparkes than any flint or calcedonie, and
therefore seemeth to deserve the name above the rest), and
besides these other stones mixed with some copper, and dailie
found upon the mountains thereabouts, will beare sufficient
witness, though I would write the contrarie."15 Harrison was
no chemist and was probably wrong about the pyrites, but still
he had wit enough to connect the character of the water with
the nature of the minerals below.
Respecting the saline, or vitriolic, decomposition of pyrites, it
is amusing to hear the opinion of Henckel, and the passage in
which he attempts to explain it is a good example of the old
doctor's verbosity :—
" Here we must premise something on the internal causality, or how the
spontaneous vitriolisation of pyrites happens internally. Philosophers might call it
magnetism, to denote a mutual action of damps and juices, on the side of the
patient, namely, the pyrites, consisting in a receptivity, and on the side of the
agent, or air, in an influx."
With the quotation of this "perplex" passage, I feel tempted
to close my remarks on Pyrites, merely adding that notwith-
standing all that has been written about this simple mineral
much still remains obscure. ''No facts in chemical geology,"
said the late Professor Newberry, "are more interesting and
mysterious than those connected with Pyrites."
GYPSUM.
Just as Pyrites is the most common of our natural sulphides, so
Gypsum is the commonest of all the sulphates. Between the two
minerals an intimate association can often be traced. On the
saline decomposition of pyrites, sulphuric acid is produced,
and by the action of this acid upon calcareous matter calcium
sulphate is readily formed. Gypsum is merely this sulphate in a
hydrated condition. Hence the marcasite of the chalk may be
accompanied by gypsum, the direct result of its own decay. So
too, in the London clay, and in other argillaceous rocks, the acid
of the decomposing pyritic mineral may re-act on the carbonate
of lime of shells and other calcareous structures of organic
15 Harrison's Description of England. Edited by F. J. Furnivall for the New Shakspeare
Society. Part I, (1877), p. 352.