678 - DR. C. CALLAWAY ON THE [ Nov. 1902, 
he observes :—‘ I think much, at any rate, of the mica is secondary.’ 
On my calling his attention to the granite-veins, he writes that he 
suspects the ‘ coarser parts’ of the slides ‘ to represent rolled-out 
- veins.’ The injection of these schists with granite-veins thus gives 
rise to a banded gneiss, of a less common type than the injection of 
granite or felsite into a basic rock. 
It will be noticed that the relations of the granite to the felsite 
and grey gneiss are similar to those described as existing between 
the granite and the rocks of the hornblendic dome. Into the non- 
schistose felsite, the granite is intruded irregularly, as into the 
diorite; but where the felsite is modified into schist, the granite-veins 
areusually lenticular. Itseems clear that the schistosity of the grey 
gneiss had been acquired previous to the intrusion of the granite 
and quartz-felsite. The posteriority of the granite to the gneiss is 
seen in the old quarry at Treflyn, east of Gwalchmai. Here a rather 
massive vein of haplite’ is intrusive in the schist. The former is. . 
unusually coarse, the pinkish-red felspar being strongly differentiated 
from the quartz: it does not display the slightest evidence of 
pressure. 
That the quartz-felsite is younger than the felsite is well seen at 
Pen-yr-argae. The dykes of the former trend.with the schistosity 
of the felsite, as if they had been intruded along the planes of least 
resistance. But the quartz-felsite is absolutely free from schistosity, 
as L have previously pointed out. 
(3) The Relations between the Felsite and the Diorite. 
The felsite does not appear in contact with the diorite in the 
central complex, except at the extreme southern end at Porth 
Gwyfen.” ‘Their relations are more clearly seen in the eastern 
eneissose band. The felsite distinctly veins the diorite at Y Graig 
(north-west of Gaerwen) and in the railway-cuttings near Llangaffo. 
It is at the latter locality that the grey gneiss (modified felsite) 
encloses isolated blocks and dyke-like masses of the diorite. It 
may fairly be concluded that the diorite is older than 
the felsite, and therefore the oldest rock in Central 
Anglesey. 
The following would seem to have been the sequence of events in 
the central complex. Diorite was first consolidated. It was then 
penetrated by masses and veins of felsite, and blocks of it were iso- 
lated from the main mass (or masses), and floated off into the felsite. 
The consolidation of the felsite was the next stage. Harth-pres- 
sures then affected both diorite and felsite, producing schistosity. 
A granitic magma, usually haplite, sometimes quartz-felsite, then 
invaded the area, penetrating the diorite and the felsite in large 
masses, and sending into them countless veins, which commonly 
1 This granite is cut by a dyke of basalt, but it has been no part of my 
purpose to notice rocks which do not affect my special enquiries. 
2 Quart. Journ. Geol. Soc. vol. liii (1897) p. 354. 
