3l8 ON THE NATURAL HISTORY 



are sometimes known from their liver-brown colour as Hepatic 

 Pyrites . 



In mineral-veins, where pyrites is often abundant, the 

 production of iron hydrate gives a rusty appearance to the vein 

 stone, and in the case of quartz reefs it suggests a kind of 

 calcination leading to the term " baked quartz." By removal of 

 the pyrites, cnbic cavities are left, containing more or less 

 ochreous iron-ore. Where the pyrites is auriferous, the precious 

 metal by resisting meteoric influences may remain in the form of 

 -sprigs or plates or grains, and hence it comes about that native 

 gold is frequently found in the rusty quartz. Professor H. 

 Louis has called attention to the fact that the iron sulphide in 

 gold-reefs is invariably cubic pyrite — never marcasite." 



The " Essex gold mine," often referred to by old writers, was 

 no doubt mythical. Yet it is not unhkely that some of the pyrites 

 •of this county may contain a trace of the noble metal. We have 

 already seen that Dale refers to its existence. He may have 

 been right ; yet there is no reason to suppose that the pyritic 

 minerals of the south-east of England contain more than a 

 minute proportion of gold, if any. Old Sir John Pettus in his 

 •" Essays on MetalUck Words," pubhshed in his Fleta Minor, in 

 1683, says, "they are exceWent five -stones which we find in our 

 mines in England, but not so good for fire-locks as those which are 

 brought from Germany, etc. And our Marcasites do neither 

 afford gold nor silver worth the charge."^' 



In mineral veins the alteration of the pyrites into limonite 

 occurs only in the upper part of the lode, above the water-level 

 of the country, or in what Posepny has called the Vadose 

 region. Below the plane of saturation, the metaUic sulphides 

 may retain their original character. The decomposition of the 

 pyrites on the " back," or outcrop of the vein, gives rise to that 

 ferruginous mass which the Cornish miner calls " Gozzan,'' and 

 the Continental miner the Chapeaude Fer or the Eiserner Hut. 

 Probably in many cases ferrous carbonate is formed as an 

 intermediate product in the production of ferric hydrate. 



II ''On the mode of occurrence of gold." Mineialogical Magazine, vol, x. (1893), 



p. 241. 



12 The title of this book Fleta has reference to the Fleet Prison, in vhich the work was 

 written by Pettus, whilst conhned, as he put it, " for my being too kind to others, and too 

 unjust to myself." As there was a legal work entitled Fleta, also because written in the 

 prison, the term minoy was added by Pettus partly for sake ot distinction and partly as a 

 play on the word miner. Pettus's puns were exceptionally weak. 



