ROCKS OF PEMBROKESHIRE. 597, 
This area is particularly referred to by the Director-General to 
prove, according to his views, the Post-Cambrian metamorphism of 
the rocks of the district that ‘‘ attended the intrusion of the granite 
and porphyries,” pp. 317-329 of his paper. In his section (fig. 2, 
p. 268) he shows the so-called granite (our Dimetian) as sending 
out from the main mass an arm (dyke) across the beds near Nun’s 
Chapel, which reaches to the Cambrian conglomerates. This dyke is 
described as one of the peripheral dykes, intimately connected with 
the granite. Even if we had not the ample evidence we now have 
to show that this conclusion is based on highly erroneous observa- 
tions, the very circumstance that not a single fact was brought 
forward by the Director-General to prove the so-called connexion 
between the Dimetian and the porphyries, ought to cause any 
thoughtful person to pause before accepting such a statement, 
made upon purely theoretical grounds. When taken to exhibit in. 
a limited sense the influence of dykes on sedimentary rocks, the 
sections at Nun’s Chapel are not of much value; as, from what has 
already been stated, the porcellanitic rocks undoubtedly owe most 
of their peculiar conditions to influences exerted at a much earlier 
period than that during which the dykes were intruded among them, 
as may be shown by abundant evidence from all parts of the district 
where they exhibit the same characters. Moreover, that these dykes 
have no connexion whatever with the Dimetian rocks is abundantly 
proved, as I shall explain further on, by our finding them cutting 
through the Dimetian at several different points. 
In connexion with the supposed nature of the so-called “ adinole” 
it is interesting to compare the analyses given by Prof. Persifor 
Frazer (at p. 18 of his paper already referred to) of the Dimetian at 
St. David’s with that given in Dr. Geikie’s paper (p. 320) of one of 
the ‘‘ Concretions,” as having been made by M. Renard. They are 
as follows :— 
‘‘ Analysis of Concretion (Adinole) Nun’s Chapel, 
St. David’s. By M. Renard.” 
IO <.. vet) w aiehrdat 24 78°62 
PEON SY cee ea lh fit. deb RRO 13°67 
RHO) yee. Sveti. Mar seete er ie 1:22 
MM Omen al it wrens) ccd vee trace 
MeO wants cad, sari hess. trace 
CaOne hese eres Bits otk hes 0-30 
Ke Ortigas Bred Ao aan te 0:26 
Naa OM. 2 hep hg ps7el5.., Rae he 5°80 
Whose) awa ee 2 0°63 
100-50 
Analyses of two specimens of Dimetian collected by Dr. Persifor 
Frazer at St. David’s, in 1882, and made in his laboratory at Phil- 
adelphia gave :— 
2n 2 
