﻿292 THE METALLOGENY OF THE BRITISH ISLES. [May 191O. 



None of the evidence for Tertiary ore-deposition in the British 

 area appears convincing, and it is concluded that the manifestations 

 of Tertiary vulcanicity and earth-movement in the area were un- 

 accompanied by the formation of ore-deposits. 



IV. Classification of the British Ore-Deposits. 



The accompanying table (p. 293) embodies the classification of the 

 ores here considered, according to their epochs and provinces, while 

 the geographical subdivisions of the Hercynian Province are also set 

 out in detail. In the various provinces there may occur deposits 

 belonging to a different epoch from that to which the characteristic 

 ores of these provinces belong. Thus, the Caledonian Province 

 of the Scottish Highlands includes some deposits belonging to the 

 } r ounger Hercynian Epoch. Again, the wolfram-bearing pegma- 

 tites of Grainsgill, belonging to the Caledonian Epoch, are in a 

 district of typical Hercynian ores. To such occurrences may be 

 applied the terms metallogenetic outlier or inlier, according 

 as they belong to a younger or older epoch than the ores charac- 

 teristic of the area where they occur. It should be mentioned 

 here that the North- West of Ireland, although its ores are 

 probably of Hercynian age, is mapped as a part of the Caledonian 

 Province (Pi. XXIII), since it is geologically related to the High- 

 lands of Scotland. Similarly, the South-East of Ireland, although 

 containing the Wicklow pyritic masses of Caledonian age, is 

 mapped as Hercynian, in order to link it up with the allied districts 

 of Northern and Central Wales, where the veins are of Hercynian 

 age. In other words, the pyritic deposits of Wicklow, considered 

 in relation to the Welsh ores and to those of Central Ireland, are 

 a metallogenetic inlier. 



V. Conclusions. 



Zones of ore-deposition. — The West of England gives much 

 insight into the nature of the Hercynian ore-formation. It appears 

 highly probable that this local development of tin-ore, with its 

 accompanying pneumatolysis, is an index of the horizon of ore- 

 deposition, and an indication of what we should find at greater 

 depths in other Hercynian districts, namely, deep-seated intrusions 

 with ores intimately related to them. As we pass up, we find 

 copper and gold in the intermediate zones, and lead and zinc in the 

 higher zones. The Cornish area thus seems to afford the key to 

 the deep-seated conditions which prevailed throughout the region 

 during the Hercynian Epoch. The occurrence in the Cornish area 

 of gold and of ores of nickel, cobalt, silver, arsenic, and antimony 

 should also be noted as throwing light on the occurrence and 

 derivation of these metals in other districts, that is, in higher zones. 

 A consideration of the data revealed in Cornwall, in the Lower 

 Palaeozoic rocks, and in the Upper Palaeozoic rocks respectively, 

 leads to the following conclusions as to the sequence of ores in 

 successive vertical zones. 



