﻿Vol. 66.1 ]\IETALLOGENY OF THE BRITISH ISLES. 297 



these islands since Armorican-movement times. As the Armorican 

 movement ceased in, at latest, Permian times, the lead-lodes of 

 Cornwall were probably formed by regional strain of the plateau- 

 type, in association with the oscillating subsidences which followed 

 the Armorican movement, and lasted until Tertiary times. These 

 movements were typified in Skye, and were possibly homotaxial 

 with the Alpine mountain-building movement of Southern Europe 

 and also anterior to it. Tin ores were found near the igneous 

 rocks, while lead ores were formed not only at a greater distance 

 but at a later time, as the Author apparently admitted in explaining 

 the connexion of the ores. The selective capacity of lead ores for 

 certain rocks caused the speaker to hesitate in accepting all the 

 Author's views. 



Mr. Postlethwaite said that he was best acquainted with the 

 ore-deposits of the Lake District, which belonged partly to the post- 

 Silurian and partly to the post-Carboniferous age. The lead ore 

 found in the Crossfell range and in the Alston District, besides 

 the deposits of haematite in Western Cumberland and Eurness, 

 belonged to the latter date ; while the lead and zinc ores found in the 

 older Ordovician rocks were of the former age. The vein-fissures 

 in the older rocks had been formed and filled before the extensive 

 denudation of the Lake District had begun. Deposits of ore, or 

 remnants of those deposits, were found on mountain-tops, notably at 

 Old Brandlehow, Barrow, and Greenside Mines. 



Mr. T. Crook congratulated the Author, but was surprised that 

 he had assigned so little active ore-deposition to the Caledonian 

 period. The visible effects of Caledonian movements on the oro- 

 geny of these islands were not less conspicuous than those of the 

 Hercynian ; while, both as regarded extent of intrusion and severity 

 of movement, the former decidedly excelled the latter. Farther, 

 the Caledonian movements probably covered a longer period of time 

 than those of the Hercynian. Therefore, according to the view 

 that periods of crust-movement synchronize with those of ore- 

 deposition, it seemed necessary to infer that the Caledonian changes 

 were probably accompanied by more productive results than the 

 Author admitted in his paper. The evidence available for assigning 

 Hercynian age to ore- occurrences in rocks which had been affected 

 by Caledonian movements seemed to be largely inconclusive. The 

 Caledonian areas had been subjected to much more extensive 

 denudation than the Hercynian ; and consequently, existing records 

 of such ore-formations as might have accompanied the Caledonian, 

 were not so nearly complete as those for the Hercynian, movements. 



Mr. Lamplugh said that the Author had correctly diagnosed the 

 state of the evidence in the Isle of Man. In a few cases it was 

 clear that the ores had attained their present position after the 

 intrusion of the Tertiary dykes, but evidence of this kind was 

 exceptional and not general. If these cases were disposed of by 

 presuming them to be due to secondary migration of ore within the 

 lode, there was very little evidence in the other lodes, including 

 the main lodes of the island, either for or against the Author's 



