OF CERTAIN EOCKS IN N.W. PEMBROKESHIRE. 355 



any of the undoubted Cambrian rocks of the district. I further 

 noticed, in following the boundaries of these so-called intrusive 

 rocks, that the junctions were mainly faulted ones. Dr. Geikie, 

 however, in his papers and elsewhere, still maintains that the views 

 indicated in the Survey maps and sections are perfectly correct. 

 Fortunately, since my last paper was read, Mr. Marr and Mr. T. 

 Eoberts have published in the Quart. Journ. Geol. Soc. vol. xli. 

 p. 476, a paper on the Lower Palaeozoic rocks of this neighbourhood, 

 which contains facts of the utmost importance in regard to the 

 questions in dispute. During their researches they noticed, in a 

 quarry near Trefgarn Eridge, an exposure of rocks of a similar 

 character to those found in the Pre-Cambrian volcanic series about 

 half a mile further north. Resting on these, quite unconformably, 

 they also found a conglomerate containing large pebbles which ap- 

 peared to have been derived from the underlying rocks. Upon the con- 

 glomerate and grit were some black shales, and in these they found 

 Olenus spinulosus and other fossils, proving them to be of the age 

 of the Lingula-flags. They also state that the shales are considerably 

 disturbed, that there are signs of faulting in the quarry, and that 

 the conglomerate adheres to the underlying " ashy-looking rock." 

 During my late visit I examined this quarry with some care, and I 

 fully concur in the interpretation given by Messrs. Marr and Eoberts. 

 I was also fortunate enough to see an exposure, in the quarry, of 

 the rock we have hitherto designated halleflinta, which is so charac- 

 teristic of the Poch and Trefgarn mountain-series. I was particu- 

 larly pleased at finding this, as it proved conclusively that the rocks 

 underlying the conglomerate could in every important particular 

 be correlated with the Trefgarn and Eoch series. This proof that 

 they extend to a distance of half a mile further south than I had pre- 

 viously indicated them is also of importance. The so-called halle- 

 llinta is now exposed on the right-hand side after entering the 

 quarry from the road ; but a heap of debris covers the face of the 

 quarry between the halleflinta and the ash-bands, so that the actual 

 contact between them is not seen. The ash is, in some places, fine 

 and compact, but at other points it is a distinct breccia. The beds lie 

 at a high angle, therefore the unconformity between them and the 

 conglomerate is most marked. The latter lie evidently on an 

 irregularly eroded surface. Specimens taken from the so-called 

 halloflintas and the ash-bands are described by Prof. Bonney in his 

 Notes on slides 1 1-1'3. In the conglomerate very large pebbles of 

 the halleflinta and of the ash are abundant. The slide No. 14 was 

 cut from a pebble over 5 inches across in one direction and 3|- in the 

 other, and Nos. 15 and 16 from pebbles measuring 2 and 3 J inches 

 across. The latter are much flattened and crushed. The similarity 

 between the halleflinta pebble and the rock in situ in the quarry as 

 well as to the rocks at Trefgarn Mountain and Eoch Castle is most 

 remarkable, and proves indisputably that the curious changes which 

 these rocks have undergone must have taken place in Pre-Cam- 

 brian times. 



This conglomerate, as shown by the fossils in the overlying shales, 



