﻿298 THE METALLOGENY OE THE BKITISH ISLES. [May I9IO. 



classification. It was necessary to recognize, however, that in 

 some cases there might be a wide difference between the age of 

 the fissure and the age of its metalliferous contents. 



The Atjthok thanked the Fellows for their reception and 

 criticisms of his paper. In reply to the President, to Prof. Watts, 

 and to Mr. Crook, who found difficulties in his view that all the vein- 

 groups that he had enumerated were of Hercynian and not Caledonian 

 age, he admitted that his conclusions were a generalization from 

 particular examples. But the community of vein-type throughout 

 the whole area, the frequent extension of a group of veins from a 

 district of Carboniferous Limestone into an adjoining district of 

 older rocks affected by the Caledonian movements, and the tracing 

 of individual veins from Carboniferous to Lower Palaeozoic rocks, 

 seemed to lead to no other conclusion than that the Hercynian 

 was the great epoch of ore-deposition in the region, always excepting 

 the area of the Scottish Highlands. It was a significant fact that 

 the great province of Caledonian granites was almost unaccom- 

 panied by closely-related ore-deposits in Britain. Ore-deposition 

 seemed to have been delayed until the next great tectonic epoch,, 

 when, strangely enough, there was, except in the Cornish area, a 

 marked poverty of plutonic intrusives (exposed). Mr. Macalister's 

 remarks suggested questions of the paragenesis of the two groups 

 of ores in Cornwall and Devon. The Author had not studied this 

 problem, but it must be considered in determining more exactly the 

 relations of the chief vein-types in that area. In the meantime he 

 interpreted ore-deposition in Cornwall and Devon as belonging to 

 one epoch (Armorican or Hercynian), the ores being deposited, 

 however, in two or more cycles. 



In reply to Mr. Lamplugh, who emphasized the importance of 

 drawing a time-distinction frequently between the formation and 

 the filling of fissures, the Author said that it was recognized that 

 the arrangement of ores in the veins was being continually modified ; 

 but their primary deposition, he felt, must have been closely con- 

 nected , in most cases, with the fissure-formation. The latter indicated 

 great subterranean energy, which must have been a factor in the 

 concentration and transport of ores in the deeper zones. Further,, 

 there was, between the Hercynian and the Tertiary, no period in 

 Britain where a deep-seated agency was manifested, which could 

 have effected the transport and deposition of ores in depth. The 

 plumosite at Foxdale, the habit of which indicated absence of 

 movement since its formation, was, he believed, either a product 

 of secondary enrichment, or the result of local re-arrangements 

 following on the Tertiary disturbances within the area of the Isle- 

 of Man. 



