S. IFi/de — Deep-mining in the Soulk-weM of Ireland. 247 



and liino veins, tlius ovidoncinf^ conditions Himilar to tlioso of otlior 

 n\inin<j; arcis whore faults and fissures, etc., occur, and havo been 

 iilled in subsociuently to tlieir occurrence. In the south of Ireland, 

 as elsewliero, tlio oblique runnin<>; veins (with relation to the strike 

 of the strata or beds) usually make ore or are mineralized. Again, 

 contra lodes or fissures which occur in the cupriferous j^rits or slates 

 (killas), and which tliomselvcs contain much disseminated copper 

 (especially the green cai'bonate), usually contain good ore, or be- 

 come good lodes. This, under the influence of time, segregation, 

 and other agencies, we should expect, and it is one of the main 

 features to be sought for in the copper-bearing region of the south- 

 west of Irt'land ; especially if the veins dip at a greater angle than, 

 the beds, though running with the strike ; and it is found, in either 

 case, in the south of Ireland, that the lodes or veins take up ore 

 from the beds through which or across which they or the fissures 

 pass. They may be very productive or the reverse, trial onl}'^ solving 

 the question ; and so long as the sides or walls of the fault or vein 

 are not permanently squeezed together, there is room for belief that 

 at different levels or depths the veins will vai'y in width and richness, 

 as in other districts. 



We must doubtless guard against confounding the so-called elvans 

 of the south-west of Ireland with those of Cornwall and other 

 locnlities — the term being used in a vague and imcertain sense in the 

 for)ner locality — whereas the elvans of Cornwall, which are of 

 undoubtedly igneous origin, and associated with the fel spathic and 

 porphyritic rocks, occur as true dykes, traversing the killas in many 

 directions and apparently almost v\dthout law. Certain light green 

 coarse sandstone, or grit bands, occurring with and differing from the 

 associated killas, are termed elvan in the south-west of Ireland, and 

 are regarded by the miners as being favourable for the production 

 and goodness of copper, especially if associated with the paler- 

 coloured greenish slates. We may draw another parallel with the 

 true mining area of Cornwall, so far as concerns the law of the 

 relation of the elvan courses to the lodes, or veins of copper in 

 the south of Ireland. In Cornwall the same coincidences are 

 observed between the lodes of copper and elvan, for in both areas 

 they usually run nearly parallel to each other, or deviate only by 

 some small angle. This is notably the case at Ballycummisk, 

 the elvafn (whatever be its nature, though doubtful if a true 

 elvan) running parallel to load No. 1 through the entire sett, but 

 crossing it to the east. We cannot, however, insist upon too close a 

 parallel on this point between the peninsula of the two islands, 

 arising from the fact that in the south-west of Ireland there are no 

 known masses of granitic or igneous rocks associated with the 

 slates and grits, and which, in the mineral districts of Cornwall, 

 have played so important a part in the impregnation of metalli- 

 ferous veins, etc. Again, we have not any true standard or evidence 

 to show the cause or the period when the Devonian rocks of the 

 south-west of Ireland became contorted and broken, there being no 

 overlying or newer rocks to give date, and no known deeper seate<l 



