112 



Professor T. G. Bonney — 



granules and very pale-green streaky or flaky spots. The latter 

 mineral is mica-like and pleocliroic, being pale yellow-ocbre colour 

 with vibrations perpendicular to the cleavage, and dull green 

 parallel with it. The tints with crossed nicols are low, and 

 extinction is either parallel to or at a very small angle with the 

 cleavage. Probably it is a chlorite. The dominant mineral of the 

 slice occurs in minute flakes closely matted, lying more or less in 

 the same direction, which show high polarization tints, pink and 

 greenish blue dominating. It is difficult, owing to their small size, 

 to determine the extinction angle, but that of a few "frayed-out" 

 scales, rather longer than the rest, was not quite straight, but 

 varied up to about 13°.' Still, notwithstanding this, I believe the 

 dominant mineral to be talc- There are a few granules of 

 magnetite. In the slice from the other specimen, though apparently 

 cut in the same general direction, the flakes run slightly larger, 

 are more confusedly matted, and the greener mineral occurs in 

 irregularly distributed patches, which do not suggest any connection 

 with veins; in one case it looks as if these might be pseudomorphic. 

 Magnetite is more abundant, both in granules and crystals, and there 

 is a grain or two of pyrite. A little calcite, obviously secondary, 

 and perhaps slightly dolomitic, occurs in one part of the slice. 

 The differences, however, between the two specimens are only 

 varietal, 



I am indebted to Miss E. Aston, B.Sc, for an analysis of the 

 more compact of the two specimens of " ovenstone," described 

 above, which she made in the Chemical Laboratoi'y at University 

 College. It is given below (No. I), and by the side I quote that of 

 a talc- schist from Anglesey,^ which I now think very possibly has 

 been formed from a serpentine (No. II). 



I. II. 



SiOa 44-94 56-34 



AI2O3 5-47 8-21 



FejOs 1-75 3-04 



Crj O3 ... ... trace ... ... - — 



Fe'O 3-47 ... ... 2-00 



CaO 8-76 0-52 



MgO 25-57 25-43 



NiO 2-90 — 



MnO trace trace 



CuO „ — 



C O3 1-22 — 



HoO 5-40 2-86 



Id. uncombined ... 0-35 



99-83 

 2-90 



(jSra2 0) 0-79 



99-19 



2-82 



S. G. ... 2-90 S. G. 



Miss Aston remarked that specimens of the rock (No. I) proved 



^ Cf. description of serpentine from the Gornergrat, Quart. Journ. Geol. Soc, 

 vol. lii (1896), p. 452. 



2 It may be an optical anomaly due to strain, or, as suggested by Rosenbuscli, to 

 an admixture with actinolite, almost identical in general aspect. I obtain the 

 results in both slices. 



^ Quart. JoiU'u. Geol. Soc, vol. xxxvii (1881), pp. 44-5. 



