114 ORIGIN AND DEVELOPMENT OF ORE-DEPOSITS. 



concentration of the ore-matter (group d), if not of actual 

 impregnation from without since their first formation (group e), 

 so that they can hardly be described as truly contemporaneous. 

 Excluding some of the tin stockworks, which as will be seen 

 hereafter have in a certain sense a claim to be considered as 

 contemporaneous ore-beds; excluding too the beds of pyritous 

 shale which exist in many parts of the district but which, hitherto 

 have not been proved to be of economic importance,''^" we have 

 only to consider in this place such interbedded ore-deposits as 

 the magnetite of Haytor, the cupriferous beds of Belstone Consols 

 and its neighbourhood, and the altered dolomite beds of 

 Ashburton and Veryan, with their manganese concentrations ; 

 together with the manganiferous slates of South Sydenham and 

 other places in Devonshire. 



Perhaps the most definite examples of bedded-ores existing 

 in the West of England are those situated at the foot of Haytor, 

 in Devonshire, and the adjoining deposits at Smallacombe — the 

 former described in 1875 by Dr. 0. Le Neve Foster,f and the 

 latter some years earlier by myself. J 



At the Haytor mine are four beds of magnetite, varying 

 from 3 to 14 feet in thickness, with a total of 26 feet or more. 

 These are interstratified with highly silicified slates and sand- 

 stones of carboniferous age — the whole series dipping pretty 

 steeply to the north-north-east, and abutting against the granite, 

 the bounding line of which runs here nearly north and south. 

 An intrusive sheet of granite is partly interbedded with and 

 breaks across the altered carboniferous strata, but the actual 

 "junction" here as in so many other places seems to be a fault 

 of a date much subsequent to the intrusion. With the magne- 

 tite, and especially near its planes of contact with the enclosing 

 slates, there is much hornblende, garnet, and axinite ; and a little 

 to the westward, at Smallacombe, the whole series is very much 



* See Boase, Trans. Eoy. Geo. Soc. Corn, iv, p.p. 176 — 191. Mr. Boase says 

 "at Tresuck iron pyrites enters so abundantly into the composition of these rocks 

 that it is entitled to be considered as a constituent, and not as an adventitious 

 mineral." (p. 191). 



f Quart. Jour. Geol. Soc, 1875, p. 628 (with references to earlier descriptions 

 in the Phil. Mag., 1827 to 1831). 



:|: Eeport Miners' Assoc, 1872, p. 71, 



