SOME ROCKS FROM CAERNARVONSHIRE AND ANGLESEY. 307 
mica, which is nearly colourless with ordinary light, but shows bright 
colours and rather ‘satiny’ texture with crossed Nicols, and is so 
remarkably like my specimens of paragonite, that I think it probably 
this mineral. The correspondence between this rock and specimens 
from Twt Hill and Anglesey is very close. 
VIL. West of Ty-Croes, Anglesey (p. 302). 
Structure similar to last, but very little mica, and that a fibrous 
mineral associated with opacite, probably replacing some other 
species. ‘The quartz rather clearer, many minute acicular micro- 
liths and a few of larger size, bordered with opacite (? titanite or 
epidote). A specimen of similar rock in my own collection exhibits 
a structure yet more irregular and unlike a true granite, and con- 
tains a fair quantity of paragonite with some minute zeolitic pro- 
ducts. 
VIII. Penbryn, near Llanfaelog, Anglesey (p. 303). 
(a) This rock, in the hand specimens, shows traces of a brecciated 
structure. ‘This is yet more distinct under the microscope ; but the 
individual fragments seem to be at most varieties of one and the 
same species of rock, and there appears very little matrix or dust 
among them; their structure varies from rather granular to fibrous 
schistose ; there are many patches of a green mineral, probably 
chlorite, and grains or rods of iron peroxide; also a few of quartz, 
to which mineral many very minute clear specks probably belong. 
With crossed Nicols, the rock is seen to be largely composed of a 
minute, rather fibrous, fairly bright-coloured mineral, possibly 
allied to sericite ; it seems to be a chloritic mica-schist. The folia- 
tion of the different fragments is not parallel, so that the brecciation 
seems subsequent to the metamorphism. 
(6) West of Ty-Croes, on road to Llanfaelog—aA specimen col- 
lected by Dr. Hicks from same neighbourhood. Similar structure ; 
varietal difference is that the fragments are rather less schistose and 
contain a little more quartz, and there is a good deal of chlorite, not 
generally in patches in the fragments, but filling veins and cracks 
between them. A part of a quartz-vein occupies a corner of the 
slide. 
TX. North-north-west of Llanfaelog church (p. 303). 
The chief difference between this and VI. is that the micaccous 
constituent is now represented by a green slightly dichroic mineral, 
probably allied to chlorite, associated with many small grains of iron 
peroxide. In the felspar are many specks and films of some secon- 
dary product, not unlike prehnite ; some, however, look more like 
a mica, 
X. Railway-cutting near Ty-Croes (p. 303). 
This rock mainly consists of felspar, chlorite, an iron peroxide, and 
calcite. The structure is more granular than one would have ex- 
pected from the external aspect, the first mineral occurring in forms 
