Vol. 60.] ROCKS OF THE KORK0WDALE VOLCANIC SERIES. 81 



on each side of Piers Gill. The Lingmell rock is a good grano- 

 phyre with crystals of uralite, derivative after augite. Large 

 plagioclases occur as phenocrysts, in a rnicropegtnatitic intergrowth 

 of quartz and felspar. Basic xenoliths similar to those of the 

 Kirkfell rocks are quite common. 



The periphery of the Lingmell intrusion is occupied by a purple 

 porphyrite. Making a good junction with this is a 

 bluish-grey garnetiferous rock. This, at first, I took to 

 be the extreme product of metamorphism of the surrounding ash, 

 but a section (3923) shows the granophyric character of the rock. 

 Similar grey garnetiferous rocks occur at the margin of the intrusive 

 rock on the left bank of Piers Gill, and also at the margin of the 

 Eskdale Granite south of Stony Tarn. 



The Piers-Gill rock (38-10) consists of quartz and felspar, the quartz 

 being developed in irregular grains. Pyrites is abundant; the pre- 

 sence of this mineral — a typical product of contact-metamorphism — 

 is suggestive. Tourmaline occurs in prisms with strong dichroism, 

 and giving straight extinction parallel to their length. Garnet in 

 rounded crystals is present, altered at the margin into white mica. 

 Quartz -porphyries with tourmaline and garnet occur at the 

 margin of the Eskdale Granite, undoubtedly intrusive into the 

 surrounding ash, so the Piers-Gill rock may be of this type. 



The main mass of the Eskdale Granite, of which that at Wastdale 

 Head is a small portion, was next visited. The granite preserves its 

 characteristic features quite close to its margin. The border itself 

 is usually occupied by agranophyre- or quartz -porphyry. 

 From the granite basic dykes are given off. These are exceedingly 

 numerous, and can be well studied in the neighbourhood of Stony 

 Tarn. They are easily distinguished by their dark colour, in con- 

 trast with the purplish tinge of the surrounding rock. The dykes 

 run east and west, or west-north-west to east-south-east, and can be 

 followed for considerable distances. One that occurs on the crags 

 immediately south of Stony Tarn can be traced almost uninter- 

 ruptedly from the granite-margin to the granite again, over a dis- 

 tance of half a mile or more. The rocks are typical diabases, 

 containing long crystals of (3878) labradorite in ophitic relation 

 with plates of uralite derivative of the augite. Kernels of augite 

 are still found. Iron-ore in minute grains is also a product of the 

 change. The uralite moreover undergoes decomposition into a 

 serpentinous product, which pseudomorphs the plagioclases. Other 

 varieties do not show any ophitic structure, the uralite occurring in 

 rotighly-idiomorphic crystals (3880). 



AVhen these dykes are traced to the granite, no intermediate 

 rocks between the diabases and the quartz-porphyry are found. 

 A great number of these basic dykes were mapped by Ward, and 

 there are probably a greater number still unmapped. They occur 

 on the lllgill side at the head of Wastwater, north of Slight Side, 

 on the south-western slope of Lingmell, and in Lingmell Gill. 

 On Yewbarrow a, series of them are mapped, and there are many 



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