ORIGIN AND DEVELOPMENT OF ORE-DEPOSITS. 339 



from an alteration of pyritous substance. At Wheal Jane and 

 Virtuous Lady such, gozzans may be traced directly down to 

 unaltered pyrites. 



The gozzans at Levant, Carn Brea, Dolcoath, and many 

 other mines, have yielded considerable quantities of tin, which 

 occurred for the most part in brilliant dark-coloured and greatly 

 modified crystals. At North Grambler the gozzan was so rich 

 for tin at the 85 fathom level that it was worked for this metal 

 at a tribute of six shilliugs in the pound. 



Blende has been obtained in large quantities at Great 

 Eetallack, Duchy Peru, Burrow and Butson, Wheal Busy, and 

 many other mines. 



Many gozzans have yielded notable quantities of chloride 

 and other silver ores, as for instance those of North Dolcoath 

 and Herland ; while gold has been found in minute particles in 

 a great many instances, though nowhere in paying quantities. 

 Nevertheless it must be admitted that in the west of England 

 gozzans are to be looked upon rather as indicators of underlying 

 deposits of value than as being themselves of economic value. 



Although the gozzan occasionally extends far below the per- 

 manent water-level of the country, yet in general this is not the 

 case. Ordinarily as soon as this water-level is reached, or very 

 soon after, the ores present (except in the case of tin, which is 

 not known as a true sulphide) are found to be almost exclusively 

 " pyritoids " (sulphides, arsenides, and the like) ; and this fact, 

 taken in conjunction with the occurrence of partially altered 

 sulphides present in the gozzan, leaves no room for doubt that 

 originally all the oxides of the gozzan — tin and some iron and 

 manganese excepted — have been derived from pre-existing 

 sulphides. 



The change of carbonate of iron into peroxide was very 

 plainly observable in the bottom of the Pawton mine near St. 

 Columb in 1874. In this case as in many others, the anhydrous 

 peroxide was formed from the carbonate notwithstanding the 

 enormous quantities of moisture present. I saw the same thing 

 in the Brendon Hills Mine, in Somersetshire, about the same time. 

 In each of these cases, too, it was plainly seen how cellular 

 quartz had been formed by the oxidation and removal of crys- 



