ASSOCIATED ROCKS OF THE LIZAED DISTRICT. 919 



vages, and is rather cracked and separated along those parallel to 



00 P. This rock contains small quantities also of an augitic mineral, 

 but much less than the other. 



Hehton Road (no. 14). — This slide shows a very pale greenish 

 serpentine, here and there a little clouded with a pale olive tint, with 

 colourless granules of olivine, a good deal of a rather fibrous mineral 

 in irregular aggregated grains, granules and dust of magnetite, and 

 larger grains of dark picotite. One or two pale brownish grains 

 show dichroism and a cleavage like that of hornblende. 



On applying polarized light the serpentine shows the usual 

 arrangement of doubly refracting meshes on an isotropic ground, not 

 much of the unchanged olivine remaining to show colours. By 

 testing the fibrous-looking mineral I have found some to be ensta- 

 tite ; but with the greater part the optic axial plane seems certainly 

 not to coincide with the plane of principal cleavage, but to make an 

 angle of about 10° with it ; I believe it to be hornblende, not dial- 

 lage. The bedded structure is indicated by a tendency to a banded 

 arrangement in the component minerals and a frequent approach to 

 parallelism in the longer diameters of prismatic- shaped crystals, and 

 of the principal cleavage-planes. Part of the slide is traversed by 

 an irregular vein filled with a steatitic mineral, which is almost 

 transparent with ordinary light, and with crossed prisms shows a 

 feebly doubly refracting granular structure. I regard it as a 

 secondary product. 



Goomldlly Downs (no. 15). — Another dull-coloured serpentine 

 with a decided banded structure. Groundmass of very pale light- 

 greenish serpentine, with numerous small angular or subangular 

 grains scattered in it rather irregularly, many aggregated dusky 

 clots, streaks and grains of magnetite, several clear brown crystals 

 with a prismatic cleavage rather like hornblende, in parts somewhat 

 dusky, with several semiopaque dusky patches of greyish and also 

 greenish colour. Small grains of picotite occur, dull olive-brown 

 and subtranslucent. With crossed prisms the field appears partly 

 dark, partly occupied by a slightly fibrous, feebly doubly refracting 

 variety of serpentine, of a dull bluish-grey colour, — chrysotile or 

 some allied variety. The grains of olivine show the usual clear 

 bright colours ; the hornblendic mineral is not brilliant ; and enstatite 

 is seen. The dusky spots show a granular structure, something like 

 the felspar pseudomorphs described above ; but of their true nature 



1 cannot be certain. The streaky structure is indicated both by a 

 tendency to grouping in parallel bands on the part of the minerals, 

 and by a parallelism in the longer diameters of the prismatic crystals 

 and the streaks of magnetite. 



Kynance Cove (no. 2). — A fine specimen kindly lent to me by Mr. 

 Allport, intermediate in character between that of Gue Graze and 

 Mullion. Some unaltered olivine, a good deal of augite or diallage (it 

 seems generally, as at Mullion, nearer the former) and perhaps a 

 little enstatite ; there are also a few semi-opaque patches which may 

 be altered felspar as at Gue Graze. With ordinary light the serpentine 

 is of a yellowish colour ; and there is a good deal of staining with a 



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