78 MR. E. E. WALKER ON THE GARNET-BEARING [Feb, I904, 



forward. The dykes which run east and west across the Hanging- 

 Knotts-Bow-Fell watershed bear a marked resemblance, in the 

 hand-specimens, to those found on the summit of Lingmell. One 

 variety might be described as being intermediate between an 

 angite-porphyrite and a granophyre — the augite occurring 

 in aggregates largely altered to chlorite ; uralite is probably an 

 intermediate product of decomposition. A similar rock runs down 

 the face of Hanging Knotts to Angle Tarn. 



A dyke running north and south along the line of Yeastyrigg 

 Crags has a central zone of bluish quartz -porphyry, the mar- 

 gins beiug occupied by a dark-green garnet-rock. This dyke gives 

 off an east-and-west branch which runs down to Yeastyrigg Gill. 

 This also is a quartz-porphyry, passing at its edges into a flinty 

 felsitic rock very hard to distinguish from the surrounding ash. 



Passim? on to the two small tributaries of the Esk which run 

 down from Esk Hause, we rind, about 200 yards down on the west 

 side of the eastern tributary, one of the most interesting dykes of 

 ?he district. This dyke was not mapped by Ward : it runs almost 

 due east and west, across the Knotts of the Tongue. 



A prominent buttress of coarsely-pitted rock stands out from the 

 surrounding rock. It varies in thickness from 2 to 3 yards, and 

 is bordered by a fine-grained, dark-green rock, with a smoother 

 weathered surface. In the coarse rock are usually to be seen 

 rounded masses, often 1 foot or more in diameter, weathering with 

 a pinkish colour : a fractured surface shows needles of a green 

 mineral in a pinkish felspar. Similar enclosed fragments also occur 

 in the line-grained marginal rock. These included fragments are 

 composed of hornblende-porphyry (3758). The hornblende 

 is in the form of long actinolite-needles, giving cofhn-shaped basal 

 sections ; the mineral is strongly pleochroic. Decomposition yields 

 chloritic iron-ore, with occasional epidote. The pink-white felspar 

 shows a pretty microperthitic intergrowth, together with albite- 

 lamellation and Carlsbad twinning, and is therefore microperthite. 

 The groundmass is a granophyric intergrowth of quartz and the 

 same felspar. Apatite is very abundant, in long needles with 

 characteristic cross-fracture. 



The coarse rock (3771) has augite in addition to hornblende ; 

 the two occurring in about equal proportions. The colourless 

 augite changes to uralite, the fibres of which show twinning relations 

 to, one another with 100 as twin-plane. An orthoclase may be 

 present among the turbid felspar, for in one or two crystals the 

 turbidity is confined to irregular patches, the rest of the crystal 

 being comparatively clear. Quartz occurs in rounded crystals with 

 a dirty outgrowth. Epidote, calcite, and chlorite are abundant. 



The fine-grained marginal rock contains augite almost to the 

 •xclusion of hornblende, and plagioclase much altered to white 

 mica. The rock is a quart z-augite-p or phy rite. The concen- 

 tration of augite in the marginal portions of the dyke is interesting. 



This dyke can be traced eastward towards the other tributary 



