920 T. G. BONNET ON THE SERPENTINE AND 



dark ruddy-brown iron peroxide. There is a steatitic band con- 

 taining enclosures of a doubly refracting variety, some of which, are 

 more like the pseudo-organic forms of Messrs. King and Rowney 

 than I have elsewhere seen, and many augitic crystals. 



Serpentine from Quarry behind Coverack Village (no. 13). — This 

 rock, as might be expected from its appearance, is, when examined 

 microscopically, a peculiar one : rather clear strings of pale gold 

 chrysotile, including not unfrequently small granules of magnetite, 

 divide the field into a number of irregular grains ; each of these is 

 subdivided by a network of yellower strings of the same mineral ; 

 these are crowded with an exceedingly fine black dust composed of 

 microliths of various forms, mostly rather granular ; and the inter- 

 spaces, often roughly quadrangular, are occupied by a colourless 

 mineral also partly filled with dust, probably magnetite. This, com- 

 monly, is aggregated, as described above, on the outer edge of the 

 interspace ; also, by bisecting the string, it often shows the position of 

 the original crack. There is no enstatite or diallage recognizable ; 

 but some fair-sized scales of a very dark brown and all but opaque 

 mineral, whose cracks are filled by colourless serpentine, may have 

 been some such mineral. With crossed prisms the larger strings 

 vary from opaque to a pale milky grey ; the smaller, commonly, 

 have a distinct golden tinge, and the interspaces are dark or very 

 pale dull milky grey. 



Dyke of Serpentine, base of Cliffs north of Kynance (no. 3). — 

 This may bo regarded as an exceptional condition of the serpentine 

 of this district ; it is very compact in structure, streaky, and red. On 

 placing it under the microscope we find that the slide consists partly 

 of roughly parallel wavy branching bands of nearly clear serpentine, 

 with a number of roundish grains, something like the eyes in a piece 

 of knotted wood, of a ruddy brown tint, inclining now and then to 

 purple ; there appears to be little or no unaltered olivine, but a fair 

 sprinkling of magnetite. On examining it with the two Nicols, we 

 find that the clearer serpentine is the feebly doubly refracting 

 variety described above, and that in most cases the browner spots 

 are slightly doubly refracting. Hardly any of the olivine has 

 escaped alteration ; but any one who has made himself familiar with 

 the other slides will have no difficulty in recognizing the charac- 

 teristic structure in the replacing serpentine. I havo no doubt the 

 rock shows a true flow structure. 



Specimen from Junction near George Cove (no. 6). — This is also 

 an exceptional variety, characterized by its exceeding compactness 

 and parallel bands of chrysotile. Under the microscope both this 

 mineral and the serpentine appear nearly colourless ; but the latter 

 contains many streaks and fibre-like aggregates of magnetite, whilo 

 the former has only occasional minute microliths included between 

 the fibres of chrys >tile, and so roughly at right angles to the sides 

 of the bands. Some dark brown subtransluccnt grains are probably 

 picotite. In one band of the slido these are rather abundant. The 

 banded structure, very conspicuous throughout this specimen, is 



