Vol. 62.] THE BUTTERMERE AND ENNERDALE GRANOPHYRE. 253 



12. The Buttermere and Ennerdale Granophyre. By Eobert 

 Heron Eastall, M.A., F.G.S., Fellow of Christ's College, 

 Cambridge. (Head January 24th, 1906.) 



[Plates XXVII & XXVIII— Microscope-Sections.] 



Contents. 



I. Introduction 253 



II. Field-Relations 253 



III. Petrographical Descriptions 258 



IV. General Characters 268 



V. Granophyric Structure 270 



VI. Summary and Conclusion 272 



I. Introduction. 



In the western part of the English Lake-District there occurs a 

 large development of igneous rocks, which are conveniently described, 

 collectively, as the Buttermere and Ennerdale Granophyre. 

 This group extends for nearly 10 miles from north to south, and 

 for nearly 5 miles from east to west. In this large area are to be 

 found several different rock-types, which present many features of 

 interest ; and, at the suggestion of Dr. J. E. Marr, F.E.S., I have 

 iindertaken the investigation of the phenomena shown in this 

 district. 



The first and only detailed description of this rock-mass was 

 given by Clifton Ward x nearly 30 years ago ; and the subject has 

 apparently never been touched as a whole by modern methods, 

 although Mr. Alfred Harker 2 has published a short description of 

 some specimens from the Wastwater district. 



II. Field-Eel ations. 



The map (fig. 1, p. 254) shows that the exposure of this group of 

 rocks is very irregular in form : to the west of Buttermere is a some- 

 what lenticular mass about 2| miles long by nearly a mile wide, 

 forming the lower part of High Stile, and the main mass of Eed Pike 

 and Gale Fell. The southern boundary of this intrusion cuts across 

 the summit of Eed Pike ; and there is a strong contrast between 

 the rugged crags of High Stile, formed of volcanic rocks of the 

 Borrowdale Series, and the smooth outlines given by the intrusive 

 rocks of Eed Pike. This intrusion is connected with a much 

 larger mass to the south by a narrow neck on Little Dodd ; and 

 this neck is very conspicuous even from a distance, by reason 

 of the weathering-out of blocks of granophyre, contrasted with the 

 peat-covered Skiddaw Slates and Borrowdale volcanic rocks on the 

 west and east respectively. 



1 Quart. Journ. Geol. Soc. vol. xxxii (1876) p. 14; also 'Geology of the 

 Northern Part of the English Lake-District' Mem. Geol. Surv. 1876, p. 31. 



2 ' Notes on North of England Eocks ' in ' The Naturalist ' 1889, p. 209. 



Q.J.G.S. No. 246. t 



