546 H, HICKS ON THE PRE-CAMBRIAN 
ConcLUSIONS. 
The evidence submitted shows most clearly that the Survey map of 
the St. David’s district and of other parts of Pembrokeshire is in- 
accurate in some of its most essential features, and in many of its 
petrographical and stratigraphical details. The present Director- 
General maintains that it ‘is in its essential features correct,” and 
that the “ officers of the Survey were certainly correct in regarding © 
the crystallme rocks which they named syenite and felstone as 
intrusive through the Cambrian strata ” (p. 291). 
He also states that this point in regard to the intrusion or non- 
intrusion of these rocks in the Cambrian sediments “is the main 
question in the present discussion” (p. 291). In his conclusions 
(p. 324) he endeavours to indicate the manner in which, and at what 
period, this took place, in the following words:—* As volcanic 
activity died out, ordinary sedimentation was resumed, and the rest 
of the Harlech and succeeding groups of the Cambrian system were 
deposited. 
*‘ At a later period the whole of these rock-groups, which had been 
laid down continuously without discordance, were subjected to dis- 
turbance, the principal effect of which was to throw them into an. 
arch, and to bend over this arch into an isocline with a general 
inclination towards the north-west. The strata likewise underwent 
a widespread foliation, which, in accordance with the structure and 
composition of the rocks affected, was chiefly developed in certain 
kinds of material. 
Cambrian, but at the latter place much to induce me to consider the Dimetian 
far the older. The finer materials of the Cambrian frequently recalled to my 
mind grits which are known to be derived from granitoid rocks. There are 
none of the usual indications of secondary metamorphism, but some, as shown 
by Dr. Geikie’s own slides, of faulting: the presence of secondary quartz proves 
nothing. I could not see any evidence in favour of the felsites being ‘ apophyses’ 
of the Dimetian, and I considered them to have broken through it. In the 
present state of our knowledge it is very difficult to say whether the Dimetian 
is or is not a granite; but I cannot admit that there is any evidence whatever 
for its being a granite of later date than the Cambrian conglomerate, and 
believe it far more ancient. Further, it appears to me that there was good 
evidence in favour of a marked physical break at the base of the Cambrian 
series. There appears to be some unconformity (perhaps much), and there is 
certainly a marked change in the lithological character of the deposits above 
and below, the ‘tuff’ bands in the Cambrian being small in comparison with 
the great mass of ordinary sedimentary materials; and, so far as I have seen, 
there is nothing to prove that they are the results of contemporaneous erup- 
tions. Besides, we do not efface the limits between Miocene and Pliocene 
because, in a country where there has been great volcanic activity in the former, 
some feeble sputterings have occurred in the latter. Lithologically your Pebi- 
dian and Cambrian at St. David’s are about as different as they can be. I 
should also like to add that from, time to time you have allowed me to examine 
the specimens used in preparing your present paper, and have lent me all the 
slides submitted to Mr. T. Davies, and I consider they establish your main 
conclusions, and I agree with his determinations in all important respects. I 
may add that the so-called ‘fine foliation’ which occurs both above and below 
the Cambrian conglomerate does not appear to me to have any bearing upon 
the question at issue. In the full sense of the words there are neither foliated 
nor metamorphic rocks at St. David's, if we exclude the Dimetian.” 
