﻿Vol. 66.] METALLOGENY OF THE BRITISH ISLES. 287 



Lake District, to which tho island is structurally related. The 

 -vein-fissures of Merionethshire and Shropshire are independent of 

 the Caledonian folds which are so well developed in these areas. 

 They generally strike across the folds, and are clearly of later date. 

 The same is true of Cardiganshire : Prof. 0. T. Jones has pointed 

 •out, for example, that the transverse vein-fissures around Pont 

 Erwyd cut across the older Caledonian folds, while the strike-faults 

 associated with these folds are barren of ores. 1 In the Leadhills, 

 the ores occur similarly in a set of conjugate fissures which strike 

 transversely to the axis of a Caledonian fold. In the Carboniferous 

 Limestone districts we find conjugate fissure-systems structurally 

 related to the post-Carboniferous compression of these areas, and 

 probably due to the stresses then set up. In none of these Carboni- 

 ferous areas do the vein-fissures extend up into adjoining Triassic 

 strata. In Ireland, for example, the vein-fissures, both in the 

 older and in the younger Palaeozoic rocks, are chiefly concen- 

 trated in those districts which were folded and compressed during 

 the Hercynian disturbances, notably in the western, eastern, and 

 southern districts. In the central plain of Ireland, where folding 

 was gentle and Assuring slight, there is an obvious paucity of veins, 

 even if we make allowance for the extensive masking by drift in 

 many places. The dependence of ore-deposits on post-Carboniferous 

 folding and consequent Assuring is thus strikingly shown in Ireland. 

 'On the whole, then, the evidence indicates that the vein-fissures of 

 these different areas are closely related, as regards both their age 

 and their origin, to the Hercynian earth-movements; while the 

 fissures in many districts of Caledonian movements are unrelated to, 

 and later than, the Caledonian structures. 



As regards the ores, their primary deposition cannot have been 

 far removed from the date of formation of the fissures. The 

 Assuring, indeed, is an index of much subterranean energy at 

 this period, while the practical absence of ores from Mesozoic 

 strata clearly points to the fact that the bulk of the ore-deposition 

 took place prior to the consolidation and elevation of these strata. 

 Further, the general community of the Hercynian type of lead, 

 zinc, and copper ores throughout the whole region, suggests that all 

 the deposits are of the same age. Conclusive evidence is obtained 

 from those areas where a type or group of veins is continuous from 

 older into adjoining younger rocks. Thus, in the Lake District,- 

 the barytic lead-veins in the Skiddaw Slates at Thornthwaite, 

 and in the Borrowdale Ashes at Greenside, are repeated when 

 we pass eastwards into the Carboniferous tract of Dufton Fell and 

 Alston Moor. Similarly, in Flintshire and in the Minera district of 

 Denbighshire, there are lead-veins in the Wenlock Shales imme- 

 diately to the west of the Carboniferous vein-districts. In the Isle 

 of Man there are veins of one and the same type in the Manx Slates, 

 in the Caledonian granite of Foxdale, and in the Carboniferous 



1 ' The Hartfell- Valentian Succession in the District around Plynlimon & 

 Pont Erwyd ' Quart. Journ. Geol. Soc. vol. lxv (1909) p. 527. 



Q. J. G. S. No. 262. v 



