Prof. T. G. Bonney—Picrite in Sark. 109 
Epidote was plentiful at some parts, as was probably also mica of 
both kinds, though it is most likely that much of the muscovite now 
seen was formed at the time when the great crushing and shearing 
took place. The same may be said of the sphene which is so plenti- 
ful in nearly all the sections, and which probably originated from 
leucoxene during the same period, together with much rutile. The 
great pressure and movement of the mass, we may suppose, also 
caused the re-generation of the decayed original felspars and the 
formation of the water-clear material which now plays so large 
a part in these schists. 
It can be seen that since the foliation took place some chlorite and 
quartz, and very large amounts of calcite have been deposited. This 
later calcite may easily be distinguished in all the sections, and 
. penetrates the rocks through and through, filling up also all the 
joints and cracks. At some outcrops it has increased so much in 
amount that it makes up most of the rock, as in the sides of the 
valley opposite 'Trenow. 
TV.—On tHe Occurrence or a Variety or Picritz (ScyELitE) 
IN SARK. 
By Pror. T. G. Bonnzy, D.Sc., LL.D., F.R.S., F.G.S. 
AST summer IJ had the pleasure of passing a fortnight in the 
Channel Islands under the guidance of my friend the Rev. H. 
Hill, who has done so much to elucidate their geology. During our 
short visit to Sark we spent some hours in the beautiful little cove 
called Port du Moulin, examining the interesting sections of the 
hornblende-schist and underlying gneissic rocks. J was wandering 
on the beach looking at the wave-worn boulders which afford most 
interesting studies of the structure of this crystalline series, when 
my eye was attracted by one which differed much from the rest, and 
resembled a dark-coloured serpentine of a slightly exceptional 
character. With some difficulty, owing to its form, I detached a 
tolerable specimen, and on examining the fresher surface, felt con- 
vinced that I had found a rock composed chiefly of an altered 
olivine and a silvery talc-like mineral. At the time it recalled to 
my memory in some respects the scyelite described by Prof. Judd, 
though it did not exhibit the conspicuous porphyritic structure of 
that rock. The conjecture proves on microscopic examination to be 
accurate, and I subjoin a short description. 
Macroscopically the rock exhibits a compact invisible-green or 
nearly black ground-mass, interrupted by specks and larger grains 
of a pale-grey mineral with a rather silky or silvery lustre; the 
grains being interrupted by black spots as is common with bastite. 
The water-worn surface shows an irregular mottling of black and 
grey. On using a lens the latter part suggests the presence of two 
minerals, one having amore fibrous structure and silky lustre; the 
other a more lamellar structure and more silvery lustre. Some 
small fakes of a brownish mica can be distinguished, and one or 
two grains of fair size are distinctly green in colour, resembling 
