284 I'ROF. T. G. BOXNEY AND MISS C. A. RAISIN ON [M.'iy 1899', 



A boss of serpentine shows a few spherules at one part ; at another 

 it contains some fair-sized crystals of rather altered enstatite, and 

 an appreciable quantity of a carbonate. It is very similar to the 

 rock next described. 



{g) North of Cerig-moelion Farm, — On a surface (about 2x2 

 feet) greenish or whitish spherules are well shown. Sometimes 

 they are developed in strings or isolated in a dark ground as 

 in the mass cl. Adjoining this part is a dark pitchy serpentine 

 containing narrow spherulitic veins. Beyond a sharp boundary, a 

 greyish-green rock with much carbonate occurs, and in it small 

 spherules are thickly clustered. This mass, like other spherulitic 

 masses, probably has been affect( d by faulting and brecciation ; but it 

 possessed previously flow-structure, as well as a brecciation, pobSibly 

 also due to the same cause. 



(/S) Microscopic Characters. 

 (1) Normal Varieties. 



Thin slices of the serpentine, when examined under the micro- 

 scope, fnquently exhibit the well-known meshM'orkstructuie de- 

 noting derivation from olivine, or sometimes the parallel close-set 

 streaks indicative of enstatite.^ Other parts show with crossed 

 nicols an irregular speckling of colours. A third variety of the 

 s'erpentine is formed of parallel close-!; et, almost vein-like bands. 

 In a fouith the slice exhibits with crossed nicols a matted mass of 

 rather narrow mica-like plates often tapering so much that the 

 sections are like spines."^ A fifth has the uniform character and 

 bluish polarization-tints, noticed in the boulder from Cruglas, and 

 attributed to alteration from enstatite (p. 281). All these forms of 

 serpentine have been already described from this district by one of us.^ 

 A specimen may show a tendency to one or other of these variations, 

 although this may have been confused by subsequent disturbance ; but 

 a mixed character is frequently setn. The 'spine '-structure is 

 most marked in the rather glittering variety described from east of 

 the road by Plas-coch (p. 280). 



The microscopic parallel banding suggests a possible fluxional 

 character.^ Even within lustre-mottled crystals it often extends 

 through neighbouring grains, and marks probably some original 

 orientation, either in the form and direction of the grains or 

 in the development of their dominant structure-planes. The 

 iron-oxide is sometimes accumulated along streaks or lines,' or it 



^ We fail to understand Mr. Blake's remark: — 'In otily one place is the 

 eerpejitine of cryfc1>i]line aspect, as in the Lizard,' Quart. Journ. Gecl. Soc. 

 vol. xliv (1^88) p. 481. In several places the texture and aspect of the ser- 

 peutine, allowing for colour-diifi^rences, is ^ery similar to that of the Lizard, 

 and, as there, bastite-crystals are not infrequent. We have not ourselvea 

 observed O'-iginal olivine reuiaining. 



^ See Quart. Journ. Geol. Soc. vol. xxxvii (1881) p. 46. 



^ Ibid. pp. 44-46. 



* Ibid. vol. xxxiii (1877) p. 920 & vol. xxxix (1883) p. 22. 



' Ibid. vol. xxxiii (1877) p. KlU. 



