ROCKS OF PEMBROKESHIRE. 547 
‘‘ Subsequent to these changes the south-eastern side of the fold 
was invaded by the rise of a mass of granite, with the usual peri- 
pheral quartz-porphyries. Accompanying and outlasting this in- 
trusion a process of metamorphism went on, the effect of which 
has been to change fine felsitic tuffs or shales into hard, flinty, 
translucent masses, and to superinduce in them a finely crystalline 
structure, with the development of porphyritic-felspar crystals and 
veins and threads of crystalline quartz.” 
He further suggests that the granite and accompanying porphyries 
may possibly represent the roots of volcanoes belonging to the 
Lower Silurian period. He may indeed well say that the question 
of the intrusion or non-intrusion of the granitoid rocks (our Dime- 
tian) into the Cambrian strata is the main point in the discussion ; 
for the general deductions, and the theories of metamorphism so 
elaborately worked out in the foregoing quotations depend entirely 
for support on the, as I have shown, mistaken supposition that the 
Dimetian is an intrusive granite of later date than the whole of 
the Cambrian rocks. I have given abundant evidence to show that 
there is no foundation whatever for such a supposition, and have 
proved by every possible kind of evidence that the Dimetian rocks 
are of very much older date than any of the Cambrian rocks. I have 
shown also that the oldest of the Cambrian conglomerates received 
much of their materials from the denudation of the Dimetian rocks, 
and that the porcellanites, which the Director-General supposes 
were mere muds or other unchanged sediments until after the whole 
of the Cambrian rocks had been deposited, were in their present 
condition in Pre-Cambrian times, as shown by the fragments of 
them in the conglomerates; also that his so-called “ adinole ” con- 
cretions are mainly fragments of still older rocks enclosed in the 
porcellanite series, and not the result of metamorphism, with a 
development of porphyritic felspar crystals in ordinary sediments, 
as claimed by the Director-General. His theory as to the so-called 
apophysial nature of the felsites also necessarily falls through, on 
the grounds alluded to above. 
Evidence has also been given which shows that the idea of the 
supposed fold in the Pebidian rocks must either have arisen from a 
process of theoretical deduction, or as the result of an exceedingly 
imperfect acquaintance with the natural sequence of the rocks and 
of the special petrological characters exhibited by the different 
members of the series. The assertions made, also, that the Cambrian 
conglomerates are conformable to the Pebidian rocks upon which 
they repose, and that ‘‘ they do not contain the characteristic rocks 
of the St. David’s district,” are amply refuted by the evidence 
given of the manner in which they are seen to overlap different 
members of the Pebidian series, and by the abundant facts produced 
in the paper and in Mr. Davies’s notes, to show that the charac- 
teristic rocks do occur in the conglomerates, as proved by macro- 
scopical and microscopical examination. 
