676 DR. C. CALLAWAY ON THE [ Nov. 1902, 
(2) The Relations between the Felsite and the Granite. 
The introduction of the new theories of metamorphism also compels 
a new reading of the band of acidic rocks which forms the eastern 
member of the central complex. Dr. Hicks’s interpretation placed 
the granite (Dimetian) at the base, followed on the east by quartz- 
felsites and halleflinta (Arvonian), which were succeeded by schists 
(Pebidian). In 1879, I formed the opinion that the quartz-felsite 
and the hialleflinta did not rank as a distinct formation, and that 
they were separated from the schist to the east by a fault, which 
appeared to be necessitated by the old hypothesis. Unhampered by 
this preconception, it is not difficult to arrive at the following 
results :— 
~ (a) The quartz-felsite forms part of the same magma as the granite. 
(4) The halleflinta (modified felsite) and associated schists are penetrated by 
the granite and the quartz-felsite in masses and veins. 
(a) The quartz-felsite forms part of thesame magma 
as the granite.—lIn 1879, I stated that the quartz-felsite occurs 
in the granite, and passes without a break into it at two localities, 
Pengarnisiog (north-east of Ty-croes) and between Tai-newydd and 
Tyn-rhos (north of Gwalchmai). Recently, I have observed a 
similar passage at the farm of Pen-yr-argae (south-west of Gwalch- 
mai). Sometimes the quartz-felsite forms distinct veins in the 
granite: this is seen to the north-west of Gwalchmai, in the Pen- 
clegyr ridge, and a little to the west of Plas-einion. 
(6) The modified felsite and associated schists are 
penetrated by the granite and the quartz-felsite in 
masses and veins.—In my descriptions under this head, I will 
include the rocks on the same line of strike to the south-west. 
Porth Nobla.—On the seashore a little to the west of this 
small bay, there is an irregular intrusion of the granite in the 
modified felsite (389) p. 666. Near at hand to the east, the felsite 
is more compressed, and is penetrated by numerous granite-veins, 
which have been rather flattened by the pressure. A little farther 
east, the veins are still more abundant, and are squeezed into thin 
seams, giving in association with the schists the appearance of 
a banded gneiss. 
South-west of Gwalchmai.—At the last ‘e’ of Pen-yr-argae, 
the granite is very clearly seen to pierce the felsite in veins. One 
of these is shown in fig. 5, p. 677. Near at hand to the east and 
north-east, the quartz-felsite is very conspicuous, cropping out in 
numerous crags, being easily recognized at a distance by its creamy 
tint. It shows no trace of schistosity ; but is extremely jointy, so 
that, though hard and sound, good hand-specimens of it are difficult 
to obtain. It penetrates the felsite, which is of a greenish colour, 
and is more or less schistose, passing towards the east and south into 
the well-marked series of quartzose and micaceous schists, which les 
to the south of Gwalchmai. Most of the intrusions of quartz-felsite 
were near the granite-mass north of Pen-yr-argae, so that they 
