268 S. Mehnore — Metamooyhisin at Cary^ock Fell. 



by local sericitization and the formation of pectolite, with extensive 

 alteration of the felsj^ars in the most intense stage. 



Evidence of similar changes is to be found in the case of the 

 interfusion rock between the gabbro and granophyre. At the foot 

 of Furthergill Syke there is a variety of this rock in which calcite 

 (without strontium) is uniformly distributed throughout the mass, 

 but otherwise corresponding to that marked " No. 2 " in 

 Dr. Harker's section across Furthergill Syke, the specific gravity of 

 which he found to be 2"805.^ The s|)ecific gravity of this altered 

 variety is 2'68. Analysis showed 0'80 per cent of carbon dioxide, 

 corresponding to 1"82 per cent calcite ; and 0'023 per cent sulphur. 

 Amongst the heaps of mine refuse at Roughtengill are to be found 

 specimens of the more basic variety of interfusion rock, containing 

 amygdules and small offshoots of calcite surrounded by a thin layer 

 of pink felspar. This calcite contains traces of strontium. 



It has long been supposed that the Carrock Fell complex represents 

 the focus of igneous activity that gave rise to the sulphide veins 

 of the Caldbeck Fells. The structural relationship and other con- 

 siderations pointing to this conclusion have been demonstrated by 

 Mr. Postlethwaite.^ Further evidence is also afforded by the way 

 in which the metallic contents of these veins fall off as we recede 

 from this centre, so that at Pottsgill and Ruthwaite the gangue 

 of quartz and barytes makes up practically the whole of the vein, 

 contents. It seems reasonable, therefore, to infer that the formation 

 of the sulphide veins is to be correlated with the tyj)e of meta- 

 morphism already described. It is noteworthy that though the 

 sulphur contents of the normal ultrabasic gabbro from Furthergill 

 Syke is considerably below the average for this type of rock, and that 

 the granophyre at the top of Carrock Fell is also low in sulphur, 

 there is, nevertheless, an increase in the amount of this element at 

 the margin of the intrusion, due either to magmatic segregation or to 

 removal of sulphides from depth by the agents that have brought 

 about the marginal metamorphism. The percentage of sulphur in 

 the rocks under consideration is : — 



Sulpliiir per cent. 

 Iron-ore gabbro . . . O'OOS 



Granophyre .... 0'014 

 Interfusion rock . . . 0-023 



SeriJentinized quarte-gabbro . 0'074 



From this point of view the sulphide veins are to be regarded as 

 contact veins in the sense of Beyschlag, Vogt, and Krusch's definition, 

 i.e. as " fissures standing open in the contact zone . . . filled with 

 ore deposited from solutions issuing from the magma ".''' 



1 Quart. Journ. Geol. Soc, vol. li, 1895, p. 133. 



- Trans. Cumb. and West. Assoc. Lit. and Sci., vol. xv, 1889-90, p. 78. 

 ^ Beyschlag, Vogt, and Krusch, " The Deposits of the Useful Minerals and 

 Rocks " ; Trans. Truscott, vol. i, 1914, p. 69. 



