Vol. 58. ] PLUTONIC COMPLEX OF CENTRAL ANGLESEY. 667 
are either roundish or lobe-like. Both quartz and felspar are 
present. Some of the mica is similar to the last, but it also occurs 
in small flakes, and in thin strings occupying cracks. The signs of 
crushing are very apparent. Prof. Bonney concedes this to be 
similar to (1) but ‘ affected by pressure.’ 
A specimen from Gwalchmai (4) has a groundmass of very 
minute irregular fragments, with microlithic mica intermixed. 
Scattered through this are large clear patches, some of them with 
rounded or lobe-like contours, others being angular. Much of this 
clear material is felspar. Prof. Bonney ‘strongly suspects’ that 
this rock is ‘the result of crushing in situ of either a felsite or a 
micro-granite.’ On the whole he ‘ inclines to the former opinion.’ 
These three slides are sufficient to prove an igneous origin for the 
rocks which bound the central granite on its eastern side. Towards 
the east, these modified felsites pass little by little into quartzose and 
micaceous schists. The passage is best seen on the shore near 
Porth Nobla, and in the district round Gwalchmai. The following 
are a few selected varieties of this schist. 
Quartz-schist (34), Ty-croes.—The quartzose and micaceous 
constituents are arranged in parallel folia. The former are in 
rounded and ijobate granules of various sizes, the larger being often 
aggregated into conspicuous lenticles. A little felspar is present. 
Most of the mica (white) is rather minute, but some of it is in 
flakes, which, running in lines parallel to the lenticles and one to 
the other, give the rock a distinctively foliated appearance. Prof. 
Bonney considers it ‘a pressure-modified quartz-felsite or micro- 
granite, and recognizes the mica as secondary. 
Quartz-schist (25), Gwalchmai.—A rock similar to that 
last-described, but the schistosity is not so well marked. It is 
regarded by Prof. Bonney as ‘ probably of igneous origin.’ | 
Typical mica-schist (461), east of Ty-croes.— Rather 
fine-grained. The water-clear constituents, which are mostly 
quartz, are in small lobate granules, and the mica (white) in either 
fair-sized microliths or flakes, the minerals being evenly arranged 
in parallel seams. There are few traces of fracture in the 
slide, the rock evidently having been almost completely reconstructed. 
Prof. Bonney thinks that the mica ‘ dates from the structure, which 
may be the result of crush.’ He is unable to decide from the slide 
whether the schist is igneous or sedimentary in origin; but raises 
no objection to the former hypothesis, if the field-evidence proves 
satisfactory. Of this there can be little doubt, since in so many 
localities schist of a similar type is seen to pass gradually into a 
rock which he admits to be igneous. 
Sound mica-gneiss (498), Porth Trecastell.—The water- 
clear constituents and the mica (white) are in larger elements than 
in the last-described slide, and the foliation is very distinct. There 
is a small proportion of untwinned felspar. A comment is made on 
this specimen by Prof. Bonney, in terms almost identical with his 
remark on (461). ; 
