322 ON THE NATURAL HISTORY 



character to the presence of pyrites : " That these baths or 

 waters are derived from such, the marchasites which the 

 Grecians call Pyvitis, pev antonomasiani (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."^^ Harrison was 

 no chemist and was probably wrong about tlie 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 

 'wliich 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 /ynY^x happens internally. Philosophers might call it 

 )nngnetism, to denote a mutual action of damps and juices, on the side of the 

 ])atient, namely, the pyrites^ consisting in a receptivity, and on the side of the 

 a ;ent, or air, in an influx." 



With the quotation of this " perplex" passage, I feel tempted 

 to close my remarks on Pyrites, merely adding tliat 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 tliis sulphate in a 

 liydrated 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 



1^ Harrison's Description of England. Edited by F. J. Furnivall for the New Shakspere 

 Society. Part I, (1877), p. 352. 



