OF CERTAIN EOCKS IN N.W. PEMBROKESHIEE. 353 



rocks of the Pebidian series show indisputably that these rocks 

 must have assumed in all important respects their present peculiar 

 conditions before the fragments were broken off (see notes on slides 

 6 and 7 by Prof. Bonney). Even the very newest of the Pre- 

 Cambrian rocks, as is abundantly clear from an examination of the 

 fragments in the Conglomerates, had been greatly crushed, cleaved, 

 and porcellanized before any of the Cambrian sediments were 

 deposited. The evidence to be obtained at St. David's therefore 

 shows unmistakably that there is a great group of Archaean rocks 

 now exposed in that area, and moreover that there is an undoubted 

 unconformity, indicating an enormous lapse of time, between the 

 lowest Cambrian Conglomerates and the underlying Archaean rocks. 



Beawdy, Haxscastle, and Beimaston. 



The so-called granite indicated in the Survey maps as having been 

 intruded into the Cambrian rocks in this area has been occasionally 

 referred to in my papers. There are no coast-sections to show the 

 nature of the contact between this so-called granite and the Cambrian ; 

 for the patch on the coast, also coloured as granite, as I shall explain 

 further on, consists of a group of felsitic rocks. The area in which 

 the so-called granite occurs is a cultivated district, and there 

 are very few exposures to be found. I have at different times 

 examined numerous points along the boundary shown on the map, 

 in order to observe the contact between the Granitoid and the Cam- 

 brian rocks ; but hitherto I have failed to meet with other than 

 faulted junctions resembling the conditions found at St. David's. 

 In no case could I find a particle of evidence to show contact- 

 alteration, or any indication whatever that the so-called granite 

 was intrusive in the surrounding rocks. During my recent visit I 

 again traced some of the lines of junction, and with the same result. 

 I could find no evidences of intrusion, but, on the contrary, the facts 

 were such as to point almost unmistakably to the Granitoid rocks 

 here being of Pre-Cambrian age, like those of St. David's. The 

 Cambrian grit seemed, in places, made up largely of a granitoid 

 debris, it being, indeed, in parts, little more than a re-arranged 

 arkose. The Granitoid rocks here resemble in many respects some 

 of those at St. David's, but on the whole contain more of the green 

 micaceous mineral. The specimens described by Prof. Bonney 

 from this area were obtained in a field near some cottages about 

 a quarter of a mile east of Troed-y-rhiw. Large and fine-grained 

 varieties are found here, as also some strongly brecciatcd bands, as 

 in Porthclais valley, near St. David's ; and an approximate junction 

 between these and some of the Lower Cambrian beds is to be seen 

 at Troed-y-rhiw and in the valley east of that point. A specimen 

 from the Granitoid rock at Brimaston was described by Mr. T. 

 Davies in his note 6 in my former paper (p. 548), and he there 

 states that it " belongs to the Dimetian type." The facts obtained 

 so far, therefore, tend strongly to confirm my view that this so-called 

 granite, whether it is of igneous origin or not, is of Pre-Cambrian 

 age and probably closely allied to the Dimetian of St. David's, 



