282 MESSRS. A. HARKER AND J. E. MARR ON 



granite ; it shows Carlsbad twinning, as well as fine lamellation on 

 the albite-law. The orthoclase is in Carlsbad twins or simple 

 crystals, lioth felspars in the larger crystals exhibit zones of growth 

 with slight variations of optical characters. 



The quartz, which in the normal granite is of anterior consolidation 

 to the orthoclase, has here been in general the latest mineral to 

 form, and occurs interstitially in wedges, or often in granular 

 patches. More rarely there is a micropegmatitic intergrowth of 

 this mineral with part of the orthoclase [1046]. Again it is not 

 uncommon to find isolated round grains of quartz, j\, to j inch in 

 diameter, with no inclusions except an occasional grain of sphene ; 

 these must belong to a rather early stage of the consolidation [984, 

 1068-1070]. 



The porphyritic crystals of flesh-coloured orthoclase which occur 

 within the dark patches are essentially identical with those in the 

 normal granite, and must belong to a rather early stage of con- 

 solidation ; but they present certain peculiarities which suggest that 

 they have been subjected to chemical corrosion by the surrounding 

 magma. They show very generally a somewhat rounded outline, 

 and frequently have a well-marked narrow border distinguished by 

 a white colour. Under the microscope it is seen that this border 

 does not consist of orthoclase, but for the most part of plagioclase 

 and quartz. The former is partly in lath-shaped forms, partly more 

 irregular, and is moulded by the quartz. All the plagioclase crystals 

 around any one orthoclase have a common orientation, presenting 

 the usual crystallographic relation towards the monoclinic felspar, 

 even when they have no point of contact with it. This fact, together 

 with the rounded outlines of the central crystal and of the whole 

 aggregate, point to the eff'ects of corrosive alteration rather than an 

 original intergrowth. It may also be observed that the border 

 contains no inclusions other than those found in the orthoclase 

 itself, as it would probably do if it were an actual addition of later 

 date. 



A singular modification of the granite is seen in a large loose 

 block to the south-east of the intrusion and just below the footpath 

 that runs along the north side of Wasdale Beck. Unfortunately we 

 have not found this type in situ. Here, on a cursory examinatioUy 

 we seem to have something very like a gradual passage from the 

 granite to a metamorphosed rock, or at least a contact of a very 

 intimate character, the two rocks dovetailing into one another in a 

 manner which makes it difficult to draw any definite line of demar- 

 cation between them. It seems as if little parallel veins of a pink 

 felspathic rock proceeded from the granite penetrating the darker 

 metamorphosed rock. In, or on the line of, these veins are large 

 flesh-coloured felspars identical with those of the normal Shap 

 granite; but the veins are sometimes too narrow to completely 

 enclose these crystals, and the felspars also occur in the line of the 

 veins beyond the point where these can be traced. The whole 

 presents a striking resemblance to a section given by Dr. Ch. Barrels* 

 * Ann. Soc. Geol. du Nord, vol. xii. (1885) p. 15. 



