﻿Vol. 66. J METALLOGENY OE THE BRITISH ISLES. 280 



sources of the Caledonian granites and of the Hercynian ore-deposits 

 respectively were closely related. 



Tertiary Epoch. — The Tertiary metallogenetic province of 

 Europe is conterminous with the Tertiary arcs of folding and 

 intrusion around the Mediterranean area. 1 The auriferous deposits 

 of Hungary and Transylvania and the ore-deposits of Italy are 

 typical examples. The Tertiary Epoch of igneous activity in the 

 north-west of the British area, however, does not appear to have 

 been accompanied by ore-deposition. These Tertiary eruptions were 

 largely of basic rocks, a type seldom accompanied by important 

 ore-deposits in Tertiary times, 2 while they did not give rise any- 

 where to thermal after-effects of any significance. Again, where 

 Tertiary intrusions occur in the British area, they are unaccom- 

 panied by ore-deposits genetically related to them. Further, the 

 distribution of Tertiary eruptives is local, and bears no relation to 

 the distribution of ores. The Tertiary volcanic rocks, indeed, are 

 concentrated in the least metalliferous portion of the kingdom. 

 Lastly, none of the British ore-deposits have any of the features 

 of the Tertiary facies, as exemplified in the andesitic and related 

 goldfields. 



It has, however, been claimed or suggested that certain of the 

 ore-deposits here classed as Hercynian are the result of the earth- 

 movements and vulcanicity of the Tertiary Epoch. The late J. G. 

 Goodchild emphasized the comb-structures and crystal-filled cavities 

 in lead-veins in the North of England as a proof that no dis- 

 turbance of the vein-fissures has occurred since ore-deposition ; and, 

 as the Tertiary volcanic period was the last phase of widespread 

 disturbance, he inferred that the ore-deposition followed these 

 disturbances. 3 These features of the veins, however, are accidental 

 rather than essential. Since the primary deposition the ores, par- 

 ticularly in the limestone districts, have undergone much solution, 

 rearrangement, and redeposition by circulating waters. Many of 

 these crystallized ores in solution-cavities are of comparatively recent 

 date, and are properly classified as secondary alterations. The 

 evidence of such structures in the veins is, therefore, inconclusive 

 and of little value as regards the age of primary ore-deposition. 

 Similarly, the plumosite of Foxdale, the delicate habit of which 

 has been taken as an indication oj: the absence of movement since 

 its formation in the vein, 4 is probably also a product of secondary 

 enrichment. The fact of movement since primary ore-deposition 

 is clearly proved by the occurrence of brecciated vein-fillings, 

 illustrated in figs. 1, 2, & 3 (pp. 290, 291). These diagrams, made 

 during the present investigation, show typical vein-structures in the 



1 L. de Launay, loc. supra cit. 



2 Malcolm Maclaren, ' Gold ' London, 1908, p. 77. 



3 ' Mode of Occurrence & Genesis of Metalliferous Deposits ' Proc. Geol. 

 Assoc, vol. xi (1888-90) pp. 45-69. 



4 G. W. Lamplugh, ' Geology of the Isle of Man ' Mem. Geol. Surv. 1903, 

 p. 503. 



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