552 E. Greenly — Quartette in Schists of Anglesey. 



Hound about them the foliated matrix sweeps in graceful curves, 

 its folia being sometimes truncated against the sides of the lentide 

 at a low angle. There is abundant quartz- veining within the body 

 of the quartzite, locally obliterating the original clastic texture; and 

 near the margin the quartz-grains are apt to he flattened, a faintly 

 schistose texture being set up in the mass. 



Lenticle of quartzite, 3| feet in length, in pale-green schist, containing many small 

 lenticles. Llansadwrn. 



Viewed as a whole, the structures reminded me strongly of those 

 in the mylonites at the Moine thrust in the North-West Highlands 

 of Scotland, except that the lenticular fragments in the latter are 

 generally (so far as I have myself seen) portions of coarse fel spathic, 

 gneissoid, or granitoid rocks. But a ni3'lonite, in which the frag- 

 ments were of rather coarse gritty sediment, would, if a certain 

 degree of crystallization were set up in the matrix, be indistinguish- 

 able from these schists. 



On reading the paper by my old colleague Mr. Lam pi ugh 

 (Q.J.G.S., vol. li, 1895) on the " Crush-Conglomerates " of the 

 Isle of Man, it appeared to me that these might yield further light 

 still upon the subject. By his kindness I have been able to study 

 the Manx phenomena in several of the most typical localities, and 

 I have but little doubt that these East Anglesey schists are 

 essentially " crush - conglomerates " whose matrix (containing 

 originally a good deal of iron and magnesia) has become crystalline. 1 

 Even in the rounding and elongation of the fragments they resemble 

 the crush-rocks of Ramsey and Sulby Glen. 2 



In the district at present mapped, I have failed to trace these 

 rocks into any unbroken sedimentary series. But that the lenticles 

 are of truly cataclastic origin, and not sheared and flattened boulders 

 in a now schistose conglomerate, is, I think, practically certain, from 

 the occurrence among them of four masses of much larger size. 

 These are the quartz-rocks of Pen-y-parc, near Beaumaris, which 



1 An explanation, practically the same, was applied by Sir A. Geikie aud Mr. 

 Peach to some rocks of doubtful age in the neighbourhood of Llangefni, Anglesey. 

 (Geikie, Pres. Address Geol. Soc. 1891, p. 130.) 



3 I have since seen the breaking up of a banded slate into rounded fragments, on 

 a small scale, though very markedly, at Llyn Padarn, Llanberis. Mr. Lamplugh, 

 however, lays stress, and I think justly, not so much on the bare occurrence of the 

 phenomenon as on its great scale and extent, in the Isle of Man. 



