Vol. 65.] INTRUSIVE BOCKS IN THE NEIGHBOURHOOD OF ESKDALE. 73 



Crag, is an offshoot of the Eskdale Granite ; but, as it will be 

 shown that dykes belonging to this series are cut and displaced 

 by those connected with the granite, and as the rocks themselves 

 are chemically and mineralogically unlike the Eskdale Granite, it 

 seems more probable that all these smaller intrusions are in- 

 dependent of, and older than, that rock. 



IV. The Dykes. 



An inspection of the 1-inch maps of the Geological Survey 

 reveals a very large number of dykes intersecting the Borrowdale 

 rocks of the district. 



These dykes are divided into three groups, namely, felsite, 

 quartz-felsite, and basalt ; and it is apparently assumed by the 

 Geological Survey (judging from the published sections) that the 

 felsite and quartz-felsite dykes are connected with the granite- 

 intrusion, the basic dykes being much later, cutting and in some 

 instances displacing the acid intrusions. 



The quartz-felsites appear to be represented by a single large 

 dyke running from Great Bank near Eskdale Green (at which 

 locality it occurs as a vein in the granite itself) by way of the 

 south-eastern slope of the Screes, where it enters the Borrowdale 

 Series, to Wasdale Hall at the head of Wastwater. Thence it 

 passes across Lin gm ell Gill and the north-western flank of Lingmell 

 to the granite-exposure at Wasdale Head, which it appears to pene- 

 trate. On the opposite side of the granite, it can be traced from 

 the neighbourhood of Burnthwaite up the side of Eskdale Eell, 

 and across the summit of Kirk Eell to Bayscar Slack, at the foot 

 of Kirkfell Crags. This appears to be .the only dyke that is un- 

 doubtedly connected with the granite-mass, with which it agrees 

 petrologically. 



The ' felsite '-dykes occur mainly in three areas : — 



(1) On Yewbarrow and High Fell. 



(2) Near Allen Crags and Angle Tarn. 



(3) Along a line from Kirkfell Crags on the north-west, by way of Peers 



Grill and Little Narrow Cove, on Scafell Pikes, to Powfell on the 

 south-east. 



The Quartz-Felsite Dyke. 



This dyke, which is, in my opinion, the only one that is connected 

 with the Eskdale Granite, consists of a reddish holocrystalline rock 

 of the quartz-porphyry group. It exhibits large and well-marked 

 porphyritic crystals of felspar and quartz, with a smaller quantity 

 of mica, in a microgranitic ground-mass. Some of the larger 

 orthoclase-phenocrysts exhibit distinct zonal structure and a 

 tendency to change into epidote. 



