374 ORIGIN AND DEVELOPMENT OF OKE-DEPOSITS. 



with silica and iron in the very stable mineral tourmaline, that 

 neither fluorine nor boron have any tin-carrying power. 

 Certainly the great bulk of tourmaline bearing rock everywhere 

 seems to be devoid of tin.f 



GrRouj? 2. — Sulphur, Arsenic, Copper, Zinc, Lead, Antimony. 



The first portion of this second group of elements is often 

 rather closely associated with the compounds of the first group, 

 but the second portion is somewhat widely diverse in its modes 

 of occurrence ; and all except perhaps arsenic occur at times in 

 considerable abundance away from the elements of the first 

 group. 



Sulphur seems to be the constant and characteristic associate 

 of the group — as much so as fluorine and boron in the first 

 group — indeed more so, for the combinations with sulphur are 

 more direct. Still it must be admitted that in our district sulphur 

 minerals are less widely distributed than are tourmaline and 

 fluor spar. 



The most extensive vein deposits of sulphides are or have 

 been the great copper veins of St. Just, Breage, Camborne, 

 Redruth, Grwennap, St. Austell, Liskeard, and the Tamar valley; 

 the great lodes of iron pyrites at Wheal Jane and Nangiles ; and 

 the large mispickel lodes of the Tamar valley. All these 

 are very closely connected with what may be called the fluorine 

 aud tin area. Sulphur is also largely associated with zinc (as 

 blende) not only in some of the districts just mentioned, but also 

 in many of the veins of galena, and in some of those yielding 

 lead and antimony. Probably, however, the greatest actual 

 amount of sulphur occurs in the large quantities of disseminated 

 iron pyrites found in the rocks of the fossiliferous sedimentary 

 series, and often far away from the tourmaline bearing rocks. 



Arsenic. The only important source of this element in 

 Cornwall is the mineral mispickel, though it also occurs to a 

 small extent in connection with nickel, cobalt, copper, and other 

 substances. The veins containing the arsenic compounds are 



f The immense deposits of boracic acid, free, or in combination with lime or 

 with alkalies, as seen in Italy and more markedly in California anrl Nevada^ 

 probably indicates the absence of the fluorine or iron necessary to fix it in the 

 mineral tourmaline, which is very rare in each of these regions. 



