554 DE. H. HICKS ON THE PRE-CAMBRIAjST AGE 



PoiNTz Castle, 



Extending along the coast south of Pointz Castle there is marked on 

 the Survey map a mass of granite. This, as I have already stated, 

 consists of a group of felsitic rocks, mainly rhyolites and breccias. 

 Some of the rocks are spherulitic, others show flow-structure, and 

 among them are some true breccias and beds of fine ash. There is 

 no granite or any rock at all approaching in character to the neigh- 

 bouring Granitoid rocks of Brawdy at present exposed there ; hence 

 the colour given in the map is highly misleading. The specimen 

 described in the note on slide 10 by Prof. Bonney was obtained by 

 me during my late visit at Cwm-bach, at the east end of the felsitic 

 group, near the point of contact with the Lower Cambrian sediments. 

 The contact here, as shown in a cliif face, is a well-marked line 

 of fault. On the north side Menevian beds and Lingula-flags are 

 faulted against the felsitic group, and there is not the slightest 

 evidence of alteration to be seen in any of the sedimentary rocks at 

 the junctions. The following are Dr. Geikie's remarks concerning 

 this area, given in a footnote to his paper at p. 292. — "Mr. Peach 

 and I had time to visit a few of the areas he [Dr. Hicks] has re- 

 named, and always with the same result. Thus, on the coast near 

 Newgale, about eight miles east of St. David's, he describes a mass of 

 Pre-Cambrian beds, chiefly ' felstones ' flanked by Cambrian con- 

 glomerates containing pebbles identical with the rocks below. All 

 that we could find was an eruptive rock penetrating and altering 

 black Cambrian shales.'" 



How Dr. Geikie could possibly have come to such a conclusion, 

 I am at a loss to understand, even if he was unaware of the fact 

 that the felsitic rocks were mainly flows and breccias ; for the junc- 

 tions are perfectly clear in good coast- sections. The Cambrian beds 

 also along the north-east edge are sandstones, grits, and fairly rough 

 conglomerates, and the latter contain fragments of felstones not to 

 be diflFerentiated from some of the rocks below. 



EocH, Pltjmstone, and Teefgaen. 



The rocks in these areas, which are coloured on the Geological 

 Survey maps as intrusive felstones, and shown there and in the 

 published section by the Survey to have produced much alteration 

 in the various surrounding rocks belonging to the Lower Cambrian, 

 Lingula-flag, and Llandeilo series, have been claimed by me on 

 various occasions as being of Pre-Cambrian age, and I have 

 contended that there is no evidence whatever to show that they 

 have been intruded into the Palaeozoic sediments, or that they have 

 produced alteration in any of the surrounding sedimentary rocks. 

 In my former papers I relied mainly on the facts obtained in ex- 

 amining the conditions at the junctions at diffej-ent points where it 

 was supposed alteration had taken place. I also found that the 

 rocks indicated as altered Lower Cambrian in the Survey section 

 were a series of volcanic rocks, ash, and breccias, greatly resembling 

 those found in the other Pre-Cambrian areas and entirely unlike 



