322 



Wood/ 1 ) This rock is therefore a biotite-hornblende-granite or horn 

 blende-granitite. 



Lake District. The granites of this district have been described by 

 Mr. WARD/*) Mr. PHILLIPS has given us some details with regard to 



D O 



the Shap granite/ 3 ) Mr. WARD recognizes three principal granite 

 masses ; those of Skiddaw, Shap and Eskdale. There is also a sub- 

 ordinate mass at Wastdale Head. The Skiddaw mass is intrusive 

 in Skiddaw slates which are metamorphosed for some distance from 

 the exposure of granite. The character of this metamorphism will be 

 described in a separate chapter. 



The Shap mass affects rocks as high as the Coniston limestone and 

 is therefore post-Ordovician. The Eskdale and Wastdale masses are 

 intrusive in the Borrowdale volcanic series. The Skiddaw mass is com- 

 posed of a grey granitite sometimes containing conspicuous porphyritic 

 crystals of a white felspar. The Shap mass is remarkable for its large 

 tabular crystals of pink orthoclase. These are almost invariably twin- 

 ned on the Carlsbad plan. They are uniformly distributed through a 

 coarse-grained granitic matrix which may be either red or grey in 

 colour. The matrix is composed of orthoclase, plagioclase, black mica 

 and quartz with magnetite, titanite, apatite and a little hornblende as 

 accessory constituents. The rock is therefore a porphyritic granitite. 

 Dark patches occur in this granite and the porphyritic felspars often 

 occur in these patches. Their angles, however, are, as a rule, more 

 rounded than in the normal granitite. In several instances Mr. PHILLIPS 

 observed that the large felspars projected beyond the boundary of the 

 inclusions into the main mass of the rock/ 4) 



tn the vast majority of cases the patches are darker in colour 

 and richer in mica and plagioclase than the normal granitite, but here 

 and there patches of a lighter colour almost devoid of black mica were 

 observed. 



The margins of the Shap mass are much finer in texture, indeed 

 the rock becomes a micro-granite in ROSENBUSCH'S sense that is, it 

 consists of porphyritic elements (quartz, felspar and dark mica) in a 

 micro- crystalline ground -mass. 



The granite of Eskdale is very different in its characters from 

 that of either of the two localities already referred to. The ferro- 

 magnesian constituent (generally dark mica) plays a very subordinate 

 part in the composition of the rock and the quartz and felspar are 

 related to each other in the same manner as they are in the rocks of 

 St. David's and Tan-y-grisiau ; that is, the quartz is frequently idio- 

 morphic with respect to the felspar or else the two minerals exhibit 

 a tendency to the micro- pegmatitic structure. Plagioclase is sparingly 



(1) See ALLPOET. G.M., Decade II., Vol. VI. (1879), p. 481. 



(2) The Geology of the Northern Part of the English Lake District. Mem. Geol. Survey, 

 1876. Q.J.G.S., Vol. XXXII. (1876), p. 1. 



(o) Q.J.G.S., Vol. XXXVI. (1880), p. 9. 

 (4) Q.J.G.S., Vol. XXXVIII. (1882), p. 216. 



