LOWER PALOZOIC ROCKS OF ANGLESEY. 583 
3. The Paleozoic rocks of northern Anglesey probably le im a 
syncline folded back to the south, those of the central band forming 
an ordinary syncline bounded on the west by an oblique fault, which 
may not materially affect the relations of the rocks on each side of 
it. 
4. There is at present no satisfactory proof that any of the fossi- 
liferous rocks of Anglesey are older than the Ordovician epoch. 
5. There is clear evidence that the gneissic rocks are of greater 
antiquity than the hypometamorphic group. , 
6. There is reasonable proof that the hypometamorphic series is of 
Archeean age. 
I am much indebted to the President for the notes which, with 
his wonted kindness, he has furnished on the microlithology of my 
paper. The arkose at the base of the Paisozoic strata of Tywyn is 
very puzzling in the field; and, without the aid of the microscope, 
it might have been difficult to convince hostile critics that the rock 
is really fragmental. This is one of these cases in which the old 
school of geologists would probably have affirmed an actual passage 
between the metamorphic and the unaltered rocks. It will, I think, 
be considered a strong confirmation of the truth of my conclusions 
that the application of microscopic tests by an independent and 
skilled observer has not materially modified any opinion which I 
had formed in the field, but has, on the contrary, added strength and 
clearness to my original convictions. 
APPENDIX. 
Nore on some Rocx-Srrctuens collected by Dr. C. CanLaway: im 
Anetrsry. By Professor T. G. Bonny, D.Sc., F.R.S., Pres. G.S. 
The following specimens have been collected by Dr. Callaway 
during his more recent investigations into the geology of Anglesey, 
and placed in my hands, together with the slides prepared from 
them, for description. In this I have kept in view their bearing 
on the more important petrological and stratigraphical questions 
rather than the determination of minute points of only minera- 
logical interest. 
110 (LTywyn ridge, p. 577).—A pinkish and greenish mottled crys- 
talline rock, whose appearance suggests that it is metamorphic 
rather than igneous. In short, it is extremely like some of the less 
coarse granitoid members of the Hebridean series of N.W. Scot- 
land. Examined with the microscope, it is seen to exhibit a marked 
fragmental structure: this, however, I have no doubt, is the result 
of crushing im situ. The finer interstitial material between the 
fragments appears to consist of dark dust, impure epidote, viridite, 
and here and there a little of a greenish micaceous mineral. The 
rock itself exhibits the structure of one of the coarse granitoid 
eneisses (such, for example, as the coarse gneiss already described 
