SERIES BETWEEN TWIT HILL AND PORT DINORWIG. 323 
suppose) of clastic origin, consisting of subangular grains of quartz, 
often rather full of very minute cavities (? empty) and specks of 
opacite, and of a quartzite varying from rather fine to moderately 
coarse, which are imbedded in a minutely crystalline matrix. This, 
when highly magnified, exhibits a felted fibrous structure, brightly 
coloured with crossing Nicols, probably formed by the alteration of 
a rather siliceous mud into microlithic products of more than one 
mineral; there are also two rather angular fragments of a fine- 
grained quartz-schist, and two or three more of doubtful origin, in 
part, perhaps, decomposed felspar. There are also some patches of 
a green chloritic mineral and, in parts of the slide, fair quantities of 
opacite. 
The rock from the quarry by* the road to Llysmeirion is also 
certainly clastic, and has some similarity to the last ; but it is more 
difficult to determine the amount of alteration. Some of the quartz 
grains (showing cayities * and included opacite) have a distinctly 
fragmental aspect ; but here and there one is seen irregularly “fused” 
at the edge with the matrix, as if formed by segregation from it. 
The matrix is earthy in aspect, and more granular in structure 
than the last, and occupies the major part of the slide; in it, 
however, there seem indications of fragments, suggesting that it 
may be composed chiefly of grains of decomposed felspar. The aspect 
of this rock suggests that it was once very probably a coarse quartz- 
felspar gritt. The rock on the southern side of the Twt-Hill ridge 
has some resemblance to this variety. 
A compact ‘* greenstone” dyke, probably a diabase (to which my 
attention was called by Dr. Hicks), is exposed in the narrow lane 
leading from the street to Twt Hill. It is about four yards wide, 
and strikes rather 8. of S.E. 
About half a mile from the quarry on the N.E. face of Twt Hill, in 
a field (used for football), is another quarry {. Here we find an in- 
teresting section exposed, which has been examined by Mr. Houghton. 
The face of the quarry is apparently formed by a bedding-plane; 
the highest stratum seen is a rather coarse conglomerate, consisting 
of pebbles ?” to 2” long, mostly round and quartzose. There are not 
a few subangular fragments of quartz, quartzite, red jasper, &c., 
and a few flat little-worn fragments of schistose rock, not unlike 
some of the Anglesey schists. Total thickness 4 feet. Below this is a 
band about the same thickness, pink-coloured at the top, grey below, 
consisting of similar material in a finer state of division. Parts of 
this are a very fine altered grit or quartzite. Beneath this is 8 feet 
of conglomerate, the pebbles being more angular than in the upper 
bed. <A considerable thickness of finer beds succeeds. Dip 45° to 
50° §.8.E. 
About 200 yards 8. of Cae-Gwyn farmhouse is another quarry, 
showing a conglomerate consisting of well-rounded pebbles (quartz, 
* Some at least of these are nearly full, as minute bubbles can be seen. 
t See Appendix to Dr. Hicks’s paper, supra, p. 806. 
{ Position on map a little S. of the “u” in “ Bathing House.” ‘The quarry 
is just on the crest of the ridge; I have recently visited it myself.—T. G. B. 
