THE SHAr GRANITE AND ASSOCIATED HOCKS. 287 



nctitc, cither original or secondary. The groundmass of felspar and 

 quartz is too far decomposed for minute examination, but it is clear 

 that the rock has been of a much more acid type than such mica- 

 traps as those found, for instance, in the Sedbergh district. 



The lowest and thickest sill, at Stakeley Folds itself, consists of a 

 quartz-porphyry in which the porphyritic elements are much more 

 crowded than in the foregoing, forming a considerable proportion of 

 the mass. The quartz grains are rounded, but with occasional 

 idiomorphic faces, and the felspars comprise both orthoclase and 

 oligoclase; The slice shows plenty of brown mica, altered into the 

 green mineral along cleavage-planes [llGl]. 



Two sills are seen near Gill Farm, farther down the same valley. 

 The lower of these two is a red quartz-porphyry with little blebs of 

 quartz. These average about Jg- inch in diameter, and have the 

 usual " corroded " appearance, with enclosures of the groundmass, 

 which is almost cryptocrystalline [1156] ; there are, moreover, 

 clusters of small porphyritic felspars like those noticed above. The 

 upper sill has to the eye a much more lamprophyric appearance. 



'Not far east of Gill Farm is a large dyke which has all the 

 appearance of an ordinary minette. No quartz is evident, but there 

 are small porphyritic felspars, usually not more than ^ inch long ; 

 some light red, others, with rounded edges, colourless and glassy. 

 These latter are found under the microscope to consist of striated 

 plagioclase with a narrow border of orthoclase, like those noted in 

 the third of the sills at Stakeley Folds. As before, the two felspars 

 have Carlsbad twinning in common [1155]. The brown mica has 

 the usual hexagonal habit, but its extinction in transverse sections 

 is oblique enough to show vaguely the repeated lamellar twinning 

 already remarked in the granite. The flakes are frequently bleached 

 in the interior, in the fashion familiar in the mica-traps of various 

 districts. The inclusions of zircon, apatite, &c. are sometimes 

 ranged parallel to the basal plane. Magnetite occurs in rather 

 large patches through the rock, as weU as in numerous minute 

 octahedra. The general ground consists largely of little felspar 

 prisms, with a few more shapeless crystals of concentrically zoned 

 felspar, and subordinate quartz. Except for the quartz in the 

 groundmass, which seems to be at least in part an original con- 

 stituent, this dyke compares closely with mica-traps such as those 

 des(5ribed by Prof. Bonuey and Mr. Houghton * in the Kendal 

 End Sedbergh districts, and by Dr. Hatch t near the latter locality, 

 or with similar rocks to be seen near Ingleton and in the district 

 west of the Cross Fell range. 



Yiewed as a whole, the set of neighbouring intrusions briefly 

 described above, while presenting a considerable range of differences, 

 have at the same time some curious points in common. Further, while 

 they have characters which seem to connect them on the one hand 

 with the Shap Fell granite, and particularly with its darker patches, 

 they, are unmistakably linked on the other hand with the normal 



* Quart. Journ. Geol. Soc. vol. xxxv. (1879) p. 165. 

 t Brit. Assoc. Eep. 1890 (Leeds Meeting), pp. 813, 814. 



