Vol. 5 I.j CARROCK FELL GRANOPHYRE AND GRAINSGILL GREISEN. 125 



15. Carrock Fell : a Study in the Variation of Igneous Rock- 

 Masses. — Part II. The Carrock Fell Granophyre. Part III. 

 The Grainsgill Greisen. By Alfred Harker, Esq., M.A., 

 F.G.S., Fellow of St. John's College, Cambridge. (Eead 

 January 23rd, 1895.) 



[Plate IV.— Map.] 



Contents. 



Part II. The Carrock Fell Granophyre. Page 



9. Introduction 125 



10. Description of the Granophyre 12b' 



11. Variation observed in the Granophyre 130 



12. Junction of the Granophyre with the Gabbro 133 



Part III. The Grainsgill Greisen. 



13. Description of the Greisen and its Relation to the Granite ... 139 



14 Possible Cause of the Modification 142 



15. Conclusion 145 



Part II. The Carrock Fell Granophyre. 



9. Introduction. 



In a former paper I have given a general sketch of the geology of 

 the Carrock Fell district, and discussed the remarkable variations 

 observed in the gabbro which is there exposed. 1 The present com- 

 munication deals with the granophyre, which is closely associated 

 with that gabbro, and with another interesting acid rock, not far 

 distant, but belonging to a different group of intrusions. 



The granophyre occurs in several distinct masses, which, from 

 their general eye-shaped outcrop and parallelism of strike with the 

 adjacent rocks, must be regarded as laccolitic intrusions (see sketch- 

 map, PI. IV.). The similarity of these neighbouring masses justifies 

 us in considering them as a connected group. The one most easily 

 studied is that which builds Carrock Fell itself, and extends west- 

 ward in a tongue nearly as far as Hound Knott. The exposures 



1 Quart. Journ. Geol. Soc. vol. 1. (1894) pp. 311-335. I take this 

 opportunity of adding a supplementary note to that paper. In describing 

 the mineralogical constitution of the gabbro, I spoke with some caution 

 of the occurrence of a subordinate rhombic pyroxene, inferred from the 

 presence of certain pseudomorphs in the rock. A subsequent study of a series 

 of slides, kindly placed at my disposal by my friend Mr. T. T. Groom, enables 

 me to conlirm this identification. One of these specimens, collected at the base 

 of the cliff, is an unusually fresh example of the gabbro, and this contains a 

 rhombic pyroxene in considerable abundance. Its relatively weak double 

 refraction, pale colour, and absence of any sensible pleochroism place it under 

 enstatite rather than hypersthene. It builds roughly idiomorphic prisms, and 

 is often in parallel intergrowth with augite. In this case the latter mineral 

 commonly borders the crystal, but little patches of augite are sometimes 

 intimately associated with the enstatite with a rude micrographic arrangement. 

 The enstatite is usually quite fresh in this slide, but in places it passes over 

 into a greenish fibrous hornblende or actinolite [2279]. 



Q. J. G. S. No. 202. l 



