74 ME. E. E. WALKER OX THE GAEXET-BEAEIXG [Feb. 1904, 



of a pink orthoclase when the rock is viewed in bulk. Eiotite 

 embraces, or hss a parallel arrangement with, the felspars, and 

 decomposes to chlorite and epidote. Apatite is most abundant 

 in this rock. 



In the last three types the groundmass becomes gradually coarser, 

 and a gradual passage is traced from a quartz-garnet- 

 porphyrite with pyrites into a true granophyre. The 

 felspar, becoming more and more abundant, finally develops into 

 irregular masses and takes part in the micropegmatitic intergrowth. 

 Slide 3863 furnishes an example of such a granophyre, containing 

 aggregates of chlorite-flakes which represent original augite. 



The most acid rock is seen on the precipitous face of Blea 

 Crag, and is also developed along the bed of Langstrath Beck, south 

 of the Stake Pass. It was mapped by Clifton Ward as an acid dyke, 

 and is undoubtedly connected with the Blea-Crag intrusive rocks, 

 for, like them, it shows perfect transition from fine-grained basic to 

 coarse acid reck. Under the microscope (37b 7 : PI. XIII, fig. 2) 

 it is seen to have a very characteristic appearance. The felspar is 

 orthoclase, occurring either in idiomorphic oblong crystals, or in 

 irregular masses. It is invariably surrounded by a microspherulitic 

 growth of quartz and felspar. Quartz occurs in irregular blebs, 

 occupying the interspaces between the spherulitic growths — chlorite 

 nearly always accompanying it. In parallel arrangement with the 

 quartz- and felspar-fibres of the intergrowth, occur elongated flakes 

 of chlorite representing original biotite. Garnet is present in 

 rounded crystals much broken and corroded, and surrounded by 

 the spherulitic growth. We have here an association which points 

 to the early consolidation of the garnet from the molten mass. 

 Apatite occurs sparingly. 



This rock varies somewhat in the relative proportions of the 

 constituent minerals; but, as a type, it is perhaps the most acid rock 

 met with in any great bulk. Xenolithsof more acid rocks do occur. 

 In Bull Crags a fragment of micropegmatite (3862) was found 

 containing quartz, orthoclase, plagioclase, and chlorite. The same 

 rock is to be seen in place as a dyke in Angle-Tarn Gill, immediately 

 above the little ravine. 



A dark-green basic rock (3861), with abundant ferromagnesian 

 mineral, was found above Bull Crags. The ferromagnesian mineral 

 is hornblende, showing strong pleochroism, the colours being 



brownish- green, brownish-green, yellow 



The felspars are altered to white mica. Oval patches of quartz 

 with a nucleus of calcite may represent original vesicles. This rock 

 is a good hornblende-porphyrite. 



A xenolith from the west side of Langstrath Beck (3b66) shows 

 idiomorphic felspars with albite and Carlsbad twinning, and possibly 

 a microperthitic- intergrowth. Small prisms of uralite, with multiple 

 twinning parallel to the orthopinacoid, occur with the same felspar 



