SPECIMENS COLLECTED IN ANGLESEY. 587 
is needless. The fragments, so far as they occur in the slides (it 
is possible a more quartziferous rock may also be present), corre- 
spond with the above-described, and the matrix consists of detrital 
hornblende and felspar, evidently derived from a similar source. 
Some of the felspar is certainly albite or oligoclase; and epidote, as 
might be expected, is present, especially in one of two fragments of 
more finely granular aspect. I think we may safely assert that the 
materials of 120-123 have not travelled far. 
124, 125 (ibid. p. 578): 126 (10 yards east of ridge, p. 578).— 
Greenish grits, composed almost wholly of fragments of metamorphic 
rocks, some resembling those last described, others approaching 
nearer to normal gneisses and to schists, with one or two of a less 
highly altered aspect. 125 contains a fragment of a schisty epido- 
site; and 124 afragment of a mineral consisting of a pale-green net- 
work with colourless interspaces; the latter dark with crossed nicols, 
the former almost so. 
127 (30 yards east of Tywyn ridge, p. 578).—Greyish-green grit. 
Constituents more varied. The felspar-hornblende rock is wanting, 
but there is one fragment of a decomposed felspar rock with a little 
of a green mineral, probably metamorphic; there are, however, the 
usual fragments of gneissic rocks, with schistose fragments resembling 
that in 117. 
129 (Llanbabo quarry, p. 569); 130 (farm west of Porth-y- 
corwg, p. 569).—Greenish-grey grits, consisting of fragments of 
quartz, felspar, a variety of schists and schistose rocks, argillites, 
“halleflintas,”’ &c. 129 contains more fragments of the less-altered 
kinds of rocks; 130 more quartz, felspar, and fragments resembling 
the more crystalline varieties described above. 
132 (Llechylched, pp. 569, 574); 133 (east of Gwredog, Rhosgoch, 
p- 569).—Brownish grits; constituents minute. These, under the 
microscope, are seen to be rather angular in form. Quartz, decom- 
posed felspar, mica, &c., with iron oxides, and the brownish-green 
mineral already described, are the principal constituents. 132 has 
more mica; 133 is more earthy and ferruginous, and has more of the 
greenish mineral. 
It may be well to state briefly the conclusions to which I am led 
by the study of this interesting series of rocks :— 
(1) The conglomerate from which specimens 120-127 have been 
collected has derived its materials from a very varied series of 
rocks. Some of these, when it was formed, were but little changed ; 
while others were considerably metamorphesed. Others, again, were 
coarse granitoid gneisses, presenting a general resemblance to the 
most ancient rocks which have as yet been discovered, such as the 
Hebridean series of N.W. Scotland or the Laurentian rocks of North 
America. Moreover these rocks were substantially in the same stage 
of metamorphism when they were rolled into pebbles as they are 
at the present time. There must then have existed at no great 
distance a land surface undergcing denudation, in which a series of 
rocks in very different states of mineralization were exposed. Thig 
