OF PYRITES AND GYPSUM. 307 



offer will therefore deal mainly with the natural history of 

 Pyrites and Gypsum. These two minerals are well developed 

 in the London Clay, and the London Clay is well developed in 

 Essex. 



PYRITES. 



Concerning Pyrites a vast deal has been written. Nearly 

 180 years ago there was published in Saxony a remarkable 

 treatise on this mineral, the work of a learned mineralogist. Dr. 

 Johann Friedrich Henckel, of Freiberg. Henckel (or Henkel) 

 was born at Merseburg in 1679. ^"^ after studying medicine at 

 Leipzig settled down in the little mining town of Freiberg, 

 where, yielding to the influence of his environment, he threw 

 'himself with enthusiasm into the study of minerals, metals, and 

 mines. He was a voluminous writer. In 1725 he publisl:ed the 

 famous work to which I have referred under the title of 

 Pyvitologia. The author died in 1744, but a new and improved 

 •edition of tlie great treatise was published posthumously, and so 

 wide became the reputation of the book that in 1757 Pyvitologia 

 was translated into Englisli, and three years later into Frencli. 



In the preface to the Englisli issue, the translator explains 

 that the work should be welcomed b}^ " those who are lovers of a 

 solid knowledge ot nature, the genuine result of observation and 

 experiment." Now it strikes me that a " solid knowledge of 

 nature " is exactly the kind of thing that will commend itself to 

 the members of the Essex Field Club. No apology therefore 

 •seems necessary for introducing Henckel's work, especially as it 

 is not likely to be famiHar to any but those few folk who happen 

 ;to be interested in the history of mineralogy. 



Although Henckel's translator, holding of course a brief for 

 ihis author, extols the Pyvitologia as " a pattern worthy of copying 

 after in our enquiries into Nature, and a just specimen of the 

 method of induction," he is yet obliged to admit that the work is so 

 prolix as to need a free exercise of editorial surgery in the matter 

 of excision. In fact the editor drops the remark that Henckel is 

 •" certainly but an indifferent writer ; diffuse to a fault, and 

 generally very obscure and perplex in his manner of writing," 

 with a " strain of low pleasantry and affectation of learning." 

 This is certainly a formidable indictment and rather tends to repel 

 the reader from attacking the great monograph ; but though one 

 -dreads having tc encounter an author who is ''obscure and 



