﻿132 ME. E. H. EASTALL ON THE [May I9IO, 



quartz-grains are the chief constituents. This sharp differentiation 

 into bands showing aluminous silicates and those consisting chiefly 

 •of quartz suggests that there has been comparatively little diffusion 

 of material, indicating a small range of molecular movement. 



In another specimen, taken about 15 yards from the granite, the 

 same minerals are shown, and cordierite is particularly abundant, 

 with the usual twinning and conspicuous inclusions of quartz, 

 of rounded form, which are so common and characteristic in this 

 mineral. The shapeless grains of andalusite often exhibit pink 

 pleochroism. Brown mica occurs in large ragged flakes, and shows 

 many pleochroic haloes. 



Another specimen, only a yard away from the granite, presents 

 some especially fine examples of twinned crystals of cordierite. 

 Although andalusite and brown and white mica are abundantly 

 present, cordierite is certainly the dominant mineral. 



I am indebted to Miss G. L. Elles for two specimens collected 

 within a few yards of the granite outcrop : one of these is a 

 peculiarly fine specimen of a cordierite-mica-schist, similar to those 

 above described, but the other is unlike anything that I have myself 

 •observed in the field. On a weathered surface it is very similar to 

 the rest, but when broken it is a pale-grey rock of very fine 

 texture. Under the microscope it is seen to consist almost ex- 

 clusively of a nearly colourless or very pale green actinolite, in 

 bundles of minute radiating needles : the colour is so pale, that it 

 is impossible to determine whether any pleochroism is shown ; the 

 extinction-angle C A Z is about 17°. There is also a very small 

 quantity of a colourless interstitial material, which may be either 

 quartz or cordierite ; the latter is more probable, but the amount 

 is too small to determine this point with certainty. This rock 

 presumably represents a thin calcareous or dolomitic layer, inter- 

 bedded with the slate. A very similar rock-type has been observed 

 in the Skiddaw Slates of Ennerdale, where they are metamorphosed 

 by the great granophy re-intrusion. 



As before mentioned, the actual contact of the granite and the 

 sedimentary rocks is well displayed in Sinen Gill, and close to 

 the junction some interesting specimens were obtained. These, 

 however, show a good deal of variation, and it is rather difficult to 

 draw up a general description. It is quite clear that both 

 arenaceous and argillaceous types are represented : in the former 

 quartz is abundant, and has apparently undergone little altera- 

 tion ; in the latter the dominant mineral is mica, either brown or 

 white. 



As an example of the highly micaceous type, we may select a 

 specimen which was taken within a few inches of the contact. To 

 the naked eye it is a brownish rock, with a conspicuously 

 crystalline appearance, though with little or no sign of schistosity, 

 and the name mica-schist, applied by the older writers, is 

 hardly appropriate. Under the microscope it is seen to consist 

 almost exclusively of flakes of mica, with a few scattered quartz- 

 grains, and a small quantity of interstitial matter, of which the true 



