SN lat 
SPECIMENS COLLECTED IN ANGLESEY. 585 
them, it is needless to dwell. It has been broken across after being 
imbedded in the matrix, which fills up the interspace (about 02 inch 
wide).’ Gneiss or granite (and I believe it to be the former), it was 
substantially what “it now 1s when it was imbedded in its present 
matrix. This exhibits the ordinary aspect of many of the clay- 
slates—an intimate mixture of brown dust. minute specks of quartz, 
and films of a greenish mineral, in which are scattered larger frag- 
ments (not generally exceeding about *01 inch in diameter) of quartz, 
a green mineral (apparently hornblende), epidote, and, perhaps, 
decomposed felspar. Some of the larger constituents appear to be 
from a granitoid rock, others from an argillite or schistose rock. 
115 (dbid. p. 578).—A mass of slaty conglomerate, the matrix 
rather darker than in the last case, with a pebble of coarse gneiss 
about 14 inch diameter. ‘The matrix has a general resemblance to 
the last described, except that there is more opacite. The smaller 
fragments also are similar: one is from a crystalline rock consisting 
of felspar (decomposed) and hornblende ; several are clearly from 
granitoid rocks; one, possibly, may be a rhyolite. A fragment 
about 3 inch diameter exhibits a distinctly foliated structure. It 
consists of a decomposed felspar, an altered brown mica, and a very 
little quartz. Only a small portion of the larger pebble i is included. 
in the slide; but this is enough to indicate that it is one of the 
usual coarse granitoid rocks already mentioned. 
116 (chid. p. 578).—A green slaty rock like the matrix of 114, 
from which, under the microscope, it does not materially differ, 
having evidently derived some of its fragments from the same 
sources. Macroscopically and microscopically, the resemblance is 
as close as possible. 
117 (Caer-gwrie, south of Clymwr, p. 571).—A fragment of a pale 
grey-green schistose rock, in a fairly coarse gritty matrix. Macro- 
scopically, the fragment much resembles 112. Examined micro- 
scopically, the similarity is not less; and to describe it would be to 
repeat the words, including the expressions of uncertainty, there 
given. This specimen also exhibits evidence of compression in the 
zigzageing of its laminse ; but I may make one remark, which seems 
to me of importance—that from the relation of these to the boun- 
daries of the fragment, I feel perfectly certain that this structure is 
not due to any pressure which the conglomerate has undergone, but 
existed anterior to the time when the fragment was detached from 
the parent rock. The matrix included in the slide is a typical 
“‘arkose,” being wholly made up of fragments of quartz and of de- 
composed felspar, with a grain or two of iron peroxide and some 
ferrite, and a greenish chloritic mineral (probably a secondary pro- 
duct after biotite), materials obviously derived from a granitoid . 
eneiss or granite. 
118 (Ridge, south of Clymwr, p. 571).—A rather coarse grit, with 
well-rolled fragments of quartz, &c., up to the size of a small pea, 
and one angular piece about 2 inches in diameter, of a schistose rock 
like that in 117. Examined under the microscope, the grit is found 
to contain fragments of more than one variety of gneiss, the usual 
