56 DR. A. E. DWERRYHOUSE ON INTRUSIVE ROCKS [Feb. 1909, 



Reference is also made to the Eskdale Granite by Mr. Harker, 1 

 who classes it with the biotite- granites, and by Dr. Teall in his 

 'British Petrography' 1888, pp. 322-23, the latter describing the 

 rock as follows : — 



' The ferromagnesian constituent (generally dark mica) plays a very siu> 



ordinate part in the composition of the rock the quartz is frequently 



idiomorphic with respect to the felspar, or else the two minerals exhibit a 

 tendency to micropegmatitic structure. Plagioclase is sparingly represented, 

 and the quartz is sometimes seen to be idiomorphic with respect to it ; a 

 somewhat unusual feature.' 



The specimen thus described, although it can be accurately 

 matched from at least two parts of the outcrop, can hardly be 

 considered typical of the Eskdale Granite, which is essentially a 

 muscovite-bearing rock and in which a felspar consisting of an 

 intergrowth of orthoelase and oligoclase is extremely common, 

 The numerous varieties of this granite will be presently described. 



Field-Relations of the Granite. 



The granite is intrusive in the lavas and ashes of the Borrowdale 

 Series, and its line of junction with these rocks is well seen at 

 intervals along its north-western, northern, south-eastern, and 

 eastern margins ; but to the westward both the Borrowdale rocks 

 and the granite are covered unconformably by the Trias (St. Bees 

 Sandstone). 



For a distance of about half a mile, from the foot of Wastwater 

 to Easthwaite Farm, the granite is in contact with the Buttermere 

 and Ennerdale Granophyre recently described by Mr. R. H. Rastall. 2 

 From the foot of Wastwater the boundary runs due south up the 

 steep slope by Pens End on to the shoulder of Whin Bigg, the 

 junction being for some distance a faulted one, and the fault-plane 

 being occupied by a vein of ironstone. The line of fault cannot, 

 however, be far from the edge of the intrusion, as the natural 

 boundary comes in on the crest of the hiB, and in several places on 

 the slope the fine-grained marginal varieties of the granite, which 

 will be more fully described hereafter, are to be seen. 



The floor of Mitredale is occupied by the granite, and in Bobin 

 Gill, a tributary of the Mite, the junction of the granite and the 

 Borrowdale rocks is seen dipping at a low angle northwards. 

 The granite becomes increasingly finer in texture as the margin is 

 approached, and undergoes at the same time a considerable change 

 in chemical composition. The Borrowdale rocks are much altered, 

 and in some places approach the condition of a mica-schist. 



From Mitredale the line of junction passes along Black Gill over 

 White Moss to Brown Band, and turns northwards by Acre Hows 

 and Eskdale Moor to the shores of Burnmoor Tarn. It then crosses 

 Hardrigg Gill at 1100 feet above O.D., the junction being visible 



1 'Petrology for Students ' 3rd ed. (1902) p. 37. 



2 Quart. Journ. Geol. Soc. vol. lxii (1906) pp. 253-73. 



