Vol. 62.] BTTTTERMERE AND ENKERDALE GRANOPHYRE. 261 



(c) The Greisen. 



On the margin of the northern laccolite, a mile west of Scale 

 Force, a curious modification of the granitic rock is to be found 

 [4764-65]. The rock here is of the coarse-textured, non-granophyric 

 type. It consists of quartz and muscovite, without felspar, but 

 with the usual chlorite in small quantity — part of the quartz is of 

 the normal type, and full of the habitual liquid inclusions ; the rest 

 of the rock consists of an aggregate of small flakes of muscovite, 

 embedded in clear quartz. In parts there is a good deal of calcite. 

 This may be described as a greisen. 



The structure is here similar to that found elsewhere at the 

 margin, and the ferromagnesian minerals and accessories are quite 

 normal. There can be no doubt that the rock originally contained 

 the usual felspar, which has decomposed, presumably under the in- 

 fluence of some pneumatolytic agent. The alkali-felspar molecule has 

 formed quartz and mica, as in the case of the Cornish greisens, while 

 the lime-felspar molecule has given rise to calcite. In some places 

 the original felspar is not quite obliterated, and still shows traces 

 of albite-twinning. 



(d) Aplitic Veins. 



At Stair Knott, on the south side of Ennerdale, the granophyre 

 is traversed by some fine-textured dykes, or veins, of rather peculiar 

 character. The macroscopic appearance of the rock is felsitic, and 

 in slices the structure is seen to be very different from that of the 

 normal granophyre. 



The rock [4760-61] consists of quartz, felspars, chlorite, and 

 various accessories. A few fairly-large porphyritic felspars are 

 present; they all show albite-twinning and generally pericline- 

 twinning also ; the angle of extinction on the albite twin-lamellae 

 varies from 0° to 20°, and the refractive indices show that the 

 composition ranges from oligoclase to albite. 



The groundmass consists of a fine-textured aggregate of small 

 grains of quartz, and rather ragged prisms of the same felspar as in 

 the phenocrysts. The chlorite also is markedly acicular, and con- 

 sequently the general appearance is somewhat trachytic. Common 

 accessories are small crystals of magnetite and haematite, prisms of 

 apatite, and small grains of epidote of various colours, generally 

 green or yellow, but sometimes colourless ; this appears to be an 

 original constituent. The amount of coloured mineral is very 

 small, and the bulk of the rock consists of quartz and felspar in 

 approximately-equal proportions. Hence, it must be of acid com- 

 position, and it is most conveniently referred to the aplite-group. 



(e) The Igneous Complex of Burtness Combe, 

 Butter mere. 



On the flanks of High Stile, on the west side of Burtness Combe, 

 occurs an interesting igneous complex on a small scale, which has 



