512 H. HICKS ON THE PRE-CAMBRIAN 
ample proof to show that the Dimetian, his so-called granite, as well 
as rocks of Arvonian and Pebidian types, had yielded very much 
of the material for the Cambrian sediments. My frequently repeated 
statements of these facts ought also, 1am fain to think, have tended 
somewhat to modify conclusions arrived at by so hasty and im- 
perfect an examination. From the paragraphs already quoted 
from the Director-General’s paper (and many others, with equally 
strong assertions of the same kind, might be quoted from it), it is 
abundantly clear that the finding of these fragments in the Cam- 
brian conglomerates at St. David’s, as in the case of those in 
North Wales, already placed before the Society, destroys the very 
pith of his argument. 
Indeed, this evidence alone is a sufficient reply to his paper; still 
I think it is due to myself and to the Society that all other evidence 
of a confirmatory character should be fully stated. This will be 
given more in detail further on, when all points where a contact 
between the Dimetian and the other rocks can be clearly seen will 
be specially referred to, and indicated, where possible, by diagrams, 
sections, or sketches. 
b. New Areas in Pembrokeshire.—The general distribution of the 
Dimetian rocks in the immediate neighbourhood of St. David’s was 
fairly indicated in my paper communicated to the Society in 1879; 
but since then J have examined an area on the opposite shore of 
St. Bride’s’ Bay where rocks of similar types occur, which will pro- 
bably prove to be of Dimetian age. Some of these rocks are coloured 
as greenstones and others as syenites, intrusive in Upper Silurian if 
not in Carboniferous beds. So far as I have yet been able to ex- 
amine these I could not find any evidence to show that the main 
masses are intrusive in Palzozoic sediments, but my examination 
tended to prove that the grits of the surrounding Llandovery series 
had been mainly derived from them or from similar rocks. One 
point, however, is abundantly clear,—that the terms greenstones and 
syenites, applied generally to these on the maps, are as utterly im- 
appropriate as in the cases at St. David’s. The only rocks which could 
possibly come under this term are some dykes of diorite and diabase ; 
but these form only a very small part of the area. The so-called 
syenite exposed at Johnston, in the railway-cutting and elsewhere 
in the neighbourhood, is a granitoid rock very similar to the Dimetian 
rock of St. David’s, and is, as there, traversed by diabase dykes. 
The so-called greenstone, well exposed on the shore of St. Bride’s 
Bay at Goultrop, Talbenny, &c., about 10 miles across the Bay 
from St. David’s, is in reality for the most part not a basic massive 
rock at all, but consists mainly of rocks with a good schistose 
foliation, and similar in many respects to some of the oldest gneisses, 
though unlike any hitherto found in the St. David’s district. These 
are described by Mr. Davies in his notes 82 and 83, and they are 
peculiarly interesting in consequence of being found in such inti- 
mate relationship with rocks of the Dimetian type. The further 
examination of these rocks may possibly lead to something definite 
in regard to the origin of the Dimetian, though of course it must be 
admitted that their age is doubtful. 
