202 PROF. T. G. BONNEY ON ROCK-SPECIMENS COLLECTED BY 
mineral; others appear to be a kind of argillite ; one or two may be 
little fragments of a mica-schist, and another possibly a decomposed 
rhyolite; but of these, without a larger number of slides, I cannot 
speak quite confidently. 
(6) Another specimen from the same conglomerate, with same 
matrix as above, and part of a pebble about 4 inch diameter. The 
latter is a granitoidite, and, except that it has rather more quartz, 
very closely resembles one of the paler varieties of that rock col- 
lected by myself near Llanfaelog (loc. cit. p. 307, no. vii.). 
(7) Bryn Golmon, east of ‘Llanerchn ymedd., is pale purplish 
quartzose compact rock, to which one might well apply the name 
“halleflinta.” On close examination it has a rather brecciated 
aspect. Under the microscope itis seen to be a fine-grained quartz- 
schist, foliation being indicated by the elongated form of the quartzes 
and by the general direction of minute films of a pale green mineral, 
probably a mica. The quartz contains numerous very minute 
cavities, generally, I believe, empty, though in one or two I think 
I detect bubbles. There is also more or less of an almost colourless 
granular dust, probably the residuum of a felspathic mineral. The 
rock has considerable resemblance to one which I have described 
for Dr. Callaway, from Bodafon mountain (Quart. Journ. Geol. Soc. 
vol. xxxvii. p. 283, no. 29. Compare also no. 25). There are 
indubitable indications of a fragmental structure, the fragments 
being more or less outlined by a black dust, some showing a dis- 
placement by the direction of their foliation-planes. Without a 
larger number of specimens I cannot positively say whether this is 
a remanié quartz-schist or one broken 2 situ by crushing ; but so 
far as I can judge, I strongly incline to the latter view. 
(8) Fragment of Conglomerate, Llyn-faelog.—tThe slide includes a 
portion of a subangular pebbie, about 4 inch diameter. This con- 
sists of grains of quartz of rather irregular outline, with the usual 
inclusions, and one crystal of white mica; no felspar is included in 
that portion seen on the slide. The pebble is probably from one of 
the more quartzose parts of the granitoidite. In the matrix are 
two or three fragments of a similar but less coarse rock, which con- 
tain kaolinized felspar. Others, yet finer, resemble the more quart- 
zose portions of a mica-schist. There is much material in the 
matrix which resembles the detritus of a mica-schist, with one 
fragment of this rock, consisting of quartz with a white and an 
altered brown mica, the latter being more or less replaced by 
chloritic minerals. I cannot precisely match this schist with any one 
that I have yet examined from Anglesey. It is not one of the dull 
lead- or green-coloured schists of the Holyhead district, but more 
resembles a mica-schist which occurs near the Menai Bridge. Litho- 
logically, however, it might very fairly be grouped with the schists 
either to the north or the south *. A fragment of argillite is pre- 
* The aspect of the matrix in the block from which the slide is cut (about 
53 4x 14 inches) would, however, lead me to believe that the dull greenish or 
lead-coloured schists near Ty-croes had contributed to the materials. 
eee 
