50 ORIGIN AND DEVELOPMENT OF ORE-DEPOSITS. 



the veins, not only as oxides (and even, though far less frequently, 

 as carbonate), but also as sulphide and sulpharsenide, in ferrugi- 

 nous blende, in chalcopyrite, in tourmaline, and in chlorite. The 

 important occurrence of iron-oxide as gozzan has already been 

 referred to. 



Manganese as a rock-constituent is rarely altogether absent, 

 though the proportion is generally very small. 



The manganese of the West of England mostly occurs as 

 peroxide, which is often associated with a great deal of iron and 

 silica. It also occurs as a carbonate and as a silicate, but its 

 affinity for sulphur or arsenic appears to be very slight. 



The peroxide is most abundant in the Devonian slates to the 

 north of Tavistock, where it occurs in the form of interbedded 

 lenticular deposits. Similar deposits have also been worked at 

 Newton St. Cyres, on the east of Dartmoor. Considerable 

 quantities of peroxide have also been met with in a vein at the 

 Euther's mine, on Tregoss Moor, None of these deposits can be 

 looked upon as exhausted, but they cannot be worked at a profit 

 at present prices. 



Nickel and Cobalt generally occur together, either in tin or 

 copper veins, associated with much ferruginous matter ; or else in 

 cross-courses near their intersections of such veins. They are 

 rarely found except in combination with arsenic. The most 

 important deposits have been met with at East Pool, Doicoath, 

 and other mines of the Camborne and lUogan district, and at St. 

 Austell Consols, but very small quantities have been found in 

 many other localities. 



The earliest notice of the occurrence of these metals which 

 I have yet come across is that of Dr. Borlase, who says that 

 nickel was found at Pengreep in Gwennap, in 1754. It was 

 discovered in a branch of a lode while driving an adit, but did not 

 hold in depth. Mr. Beauchamp got the Society of Arts prize of 

 £30 for the best nickel-ore raised in England.* 



Pryce, writing 20 years later, said that Cobalt had been 

 found at Trugo in St. Oolumb, in a vein from 4 to 6 inches 

 thick, where it crossed a copper lode, but only continued for a 

 short distance. It was then considered to be worth £60 per ton. 



* Borlase, Nat. Hist. Corn., p. 130. 



