‘ 
454 E. B. Tawney—Woodwardian Laboratory Notes. 
arises from the veins of chrysotile having a roughly parallel 
direction; they cut straight through the ground, and the augites. 
The microscope shows these veins of rhombic chrysotile to constitute 
an important fraction of the rock; they are not all parallel. The 
augite is pretty fresh in its normal condition, but some of it is 
full of bundles of curved capillary lines, mostly parallel in two 
intersecting directions, so crowded as to render the augite quite 
fibrous-looking; they seem to me minute cracks rather than fibres, 
the slenderer ones exceedingly delicate. There are lines of brownish 
elongated inclosures, three or four deep, occasionally present, which 
seem in no fixed relation to the prismatic cleavage. The plagioclase 
prisms retain their striations, but many are decomposing ; patches of 
granulated zeolitic matter covering a considerable part of the slide 
have no doubt been formed from them, some radiating and showing 
bright aggregate polarization. ‘There are also greenish and dirty 
brownish green tracts due to decomposition of the augite probably ; 
the green areas where fibrous show bright aggregate polarization ; 
the dirty grains with ferruginous staining are probably another part 
of the same process. 
[P. T71.] Gimblet Rock (Carreg y rimbill), Pwlihelii—This rock, 
which forms a boss at the entrance of the harbour terminating the 
sand-hills, is largely quarried for “‘sets”’; its divisional planes have 
been noticed by Professor Bonney (Q.J.G.S. vol. xxxil. p. 145). In 
the hand-specimen it is a speckled brown and white rock of medium 
grain, owing to the large sheets of bronzy pyroxene, with cleavage 
planes of metallic lustre, being interrupted and penetrated by the 
numerous felspar crystals which protrude in all directions through 
them. Abundant effervescence with acid. From the nature of the 
pyroxene it must be classed as a diabase. 
Microscope.—The pyroxene is in large sheets, interpenetrated by 
the felspars; it is pale yellow in the slice; the cleavage not very 
constant, and not pinacoidal. A most noticeable feature are lines of 
minute inclosures, which, when magnified 400 diameters, are seen to 
be minute grains of irregular form and yellowish ferric colour ; these 
being several deep form broad lines which cross the cleavages at all 
angles, apparently, according to the direction of the slice; they are 
undulated, sometimes branching, but usually roughly parallel to each 
other,—it is better developed here, but the same feature as in the 
slides [P. 58], and that from Deneio: only where the augite is 
fibrous from incipient decomposition does it simulate diallage: from 
this stage it passes to a clear feebly dichroic chloritic mineral, and 
then into an irregular fibro-granulated dirty green substance, with 
aggregate polarization. The plagioclase is partly fresh, but the 
centres of most of the crystals are converted to a white opaque 
substance; they are much traversed by viridite veins in places. 
A little brown mica, strongly dichroic, is present; some flakes, 
apparently in the centre of decomposed augite, point rather to its 
derivation therefrom; others connected with erystals of black iron- 
oxide do not show so plainly any relation to the augite: the 
iyon-oxide from its form Seems probably. ilmenite, but is free from: 
