ORIGIN AND DEVEL0P3IENT OF ORE-DEPOSITS. 153 



vughs ; mineral springs ; local chemical action ; extensive local 

 alterations of lode-substance and country rock and the like. 

 Some of these phenomena have been already referred to with 

 sufficient detail, of others which have been developed in a more 

 marked manner in other localities, it may be well here to give 

 references to some select examples. 



"Oontact deposits," that is rich parts of the lode bounded by 

 different rocks on the hanging and foot-walls, though existing 

 in places, are not particularly noticeable either in Dolcoath or 

 Perran lodes. The great fiat lode however on the other side of 

 the Carn Brea range affords notable examples in most of the 

 mines (see fig. 10, Plate in), so also many of the copper-lodes in 

 the Gwennap district which frequently had their rich parts 

 bounded on one side by killas and on the other by elvan. 

 Similar contact deposits having slate on the hanging wall and 

 granite on the foot-wall are common in the copper lodes of the 

 Caradon district.* 



"Intersections" and their remarkable effects on the lode are 

 particularly noticeable in the Perran lode, as already mentioned ; 

 there are many too of much importance in connexion with the 

 Dolcoath lode, while many of them are accompanied by notable 

 heaves — as in the case of the great cross-course between Dolcoath 

 and Cook's Kitchen, which heaves the lode many fathoms to the 

 right. The most remarkable, if not individually the most 

 extensive examples of heaves, however, are perhaps those of the 

 St. Agnes district, where they have been most carefully and 

 accurately described by several observers — and notably by 

 Mr. A. T. Davies in 1879. f Further reference to this part of 

 the subject will be made in the fifth chapter. 



The "good and bad directions" of the rich and poor parts of 

 the copper-bearing parts of Dolcoath have been already referred 

 to in quotations from lectures by Capt. Chas. Thomas. Similar 

 phenomena were very marked in most of the Grwennap copper 

 mines — they are traceable but not so marked in many of the tin 

 mines. 



* See Foster, Great Flat Lode, Quart. Journ. Qeol. Hoc, xxxiv, p' 640, 

 1878, and Henwood, Trans. Roy. Geol. Soc. Corn., viii. 

 fOn heaves and faults. Eep. Miners Assoc. 1879. 



