116 ORIGIN AND DEVELOPMENT OF OEE-DEPOSITS. 



clierty -looking rock — shewing its origin plainly under the micros- 

 cope, and containing in one instance over 95 per cent, of silica.* 



The silica of these rocks has something of a chalcedonic 

 character, shewing very few traces of crystallization. The same 

 period and mode of silicification is perhaps indicated by the 

 occurrence in the neighbourhood of the rare mineral Haytorite 

 — which is a chalcedonic pseudomorph after Datholite. 



A somewhat similar association of bedded magnetite with 

 hornblende, axinite, and apatite interstratified with "greenstone 

 slate" or "hornblendic slate" occurs at the Crown's Mine, Botal- 

 lack, and was briefly described and compared with the well-known 

 Perseberg deposit in Sweden by Dr. Foster, in 1867.f Similar 

 beds of magnetite have been worked to a small extent at Trelus- 

 well, near Penryn, and at Brent, in Devon. 



The nodules of argillaceous iron-stone associated with the 

 bands of sandstone, shale, and anthracite, of the " carbon series 

 near Bideford, reminding us of the intermixture of iron-ore and 

 vegetable matter in the bogs and morasses of the present day," 

 were referred to by Sir H. Delabeche maoy years since, | but 

 they have never, I think, been worked. 



The red hematite of the Permian rocks in the neighbourhood 

 of Luckham and Wotton Courtney, in West Somerset, has been 

 "in some localities worked in the manner of a quarry for that 

 ore, and profitably exported in the state in which it is thus roughly 

 obtained .... the hematite constituting as much a part of the beds 

 as the sandstone and conglomerates with which it is associated. "§ 



Another series of metalliferous beds, of considerable geolo- 

 gical if not economical importance, occurs on the north side of 

 Dartmoor, and extends from Sourton to South Zeal — a distance 



* The practical importance of this silicification to the miner was shewn by 

 the fact that the adit driven from the Smallacombe side for the purpose of opening 

 up the magnetite beds in depth cost in some parts over =£50 per fathom in driving. 

 This however was before the use of boring machinery and of dynamite had 

 become at all general in the West of England. 



t Report Miners' Association, 1867, p. 46. 



;j; Report on Cornwall, &c., p. 125. At page 143 he says on the same series of 



deposits " The general character of the great carbonaceous deposit of Devon 



...... is that of drifted matter, vegetable remains included in this respect 



it appears unlike the coal deposits of Northumberland and Durham " (p. 143) , 



§ Ibid, p. 197, 



