Vol. 65.] TS THE NEIGHBOURHOOD OF ESKDALE. 65 



shows a somewhat unusual type of micropegmatitic structure. 

 This consists of a growth of quartz about a much-decomposed 

 crystal of oligoclase ; the quartz, although very irregular in 

 form, is apparently a single crystal, as all parts of it extinguish 

 simultaneously ; it is penetrated by smaller individuals of a felspar, 

 which I was unable to identify, in true micropegmatitic fashion. 



Specimen54 is a similar rock to No. 53, but rather deeper in 

 colour and with the porphyritic elements less conspicuous. It 

 contains a few minute flakes of muscovite which, however, appear 

 to be secondary. 



Marginal varieties from Hardrigg Gill. — The various 

 marginal types are well exposed in Hardrigg Gill, and specimens 

 78, 79, 80, 80 a, 80 b, & 81 were collected in the stream, 78 being 

 farthest from the edge of the intrusion, while 81 was an actual 

 junction-specimen. These specimens are described somewhat fully, 

 as they constitute the best series of the marginal varieties which 

 have been collected. 



Specimen 78. — A medium-grained granite consisting of quartz, 

 pink felspar, and a greyish mica. 



The minerals are quartz, perthite, oligoclase, biotite, and 

 muscovite, with apatite as an accessory. The biotite and musco- 

 vite are in parallel intergrowth, and the former has passed over 

 into a green decomposition-product, apparently chlorite. The 

 muscovite is present in large amount, as compared with the biotite. 

 There are some minute particles, of a brownish-yellow mineral 

 resembling augite, in one part of the section. 



Specimen 79 (see chemical analysis, p. 64). — Less even in 

 texture and somewhat finer-grained than 78, grey in colour, and 

 showing larger grains of quartz and nests of mica. 



The minerals are green biotite with muscovite in parallel inter- 

 growth, perthite, oligoclase, and quartz. Threads of muscovite 

 appear to run off from some of the larger crystals into the crystals 

 of perthite. Micropegmatitic structure occurs, but only to a small 

 extent. 



Specimen 80 (see chemical analysis, p. 64; also PI. Ill, fig. 4). — 

 A rock of fine-grained granitic texture, but consisting almost 

 entirely of quartz, with a few greenish veins traversing it. It is a 

 fine-grained mosaic of quartz, with a few minute flakes of muscovite. 

 The grains of the mosaic average 0*25 millimetre in diameter. 

 Felspars and biotite are absent. The specific gravitv of the rock 

 is 2-62. 



Specimen 80a. — Slightly darker in colour and coarser in 

 texture than No. 80, but consisting of quartz with minute 

 wisps of muscovite, and a small quantity of ilmenite apparently 

 associated with the muscovite. 



Specimen 80 b. — Similar in texture to No. 80 a, but pink in 

 colour. It is an aggregate of quartz and perthite, with a less 



Q. J". G. S, No. 257. 3P 



