VOLCAMIC SERIES OP ST. DAVIDS. 249 



The Pebidian strata at Ogof Golchfa, which are troubled by a 

 basic igueoiis iutrusion, show as clearly as, if not more clearly than, 

 at St. jVon's Bay the incoming of sedimentary conditions. They are, 

 indeed, marked on Mr. Blake's plan (Quart. Journ. Geol. Soc. vol. xl. 

 p. 298) as " Cambrian sandstone." They consist of red and purple 

 and green sandy and very close-grained tuffs. In hand-specimens 

 the finer red beds are scarcely if at all distinguishable from the red 

 Lingula-jprimceva beds of the Cambrian of this district. They are, 

 however, remarkably schistose, but not more so than the finer heels of 

 the conglomerate itself. I cannot make 5° difference between the 

 strike of the Pebidian strata and that of the overlying conglomerate. 

 Both are N. 35° E. The dip of the conglomerate at the seaward 

 low-tide face is 45°, near the faulted junction it is bb° ; that of the 

 Pebidians is from 00° to 70°, or even somewhat higher. 



Here, then, we have, together with some slight signs of local 

 unconformity, a marked parallelism of strike, a continuous change 

 of dip, and a common schistosity. I could find absolutely no 

 evidence of the divergence of no less than 45° between the strike 

 of the conglomerate and that of the Pebidian drawn by Dr. Hicks 

 on his map. The strike of both can be readily observed at Ogof 

 Golchfa, and they are practically identical. 



e. In Ramsey Sound. — ■J^J'ear Ehoson the conglomerate may be 

 seen in the first field going down to Porth Stinian, to the left of the 

 path. The strike here is N". 45° E. ]N"o junction with the Pebidian 

 can be seen, but these strata near the farm and on the flagstaff- hill 

 appear to have the same strike. The Pebidian on Rhoson, more- 

 over, and the conglomerate in the field both have a low dip of from 

 25° to 35°. 



There are several field-exposures of the conglomerate between 

 E-hoson and Maen Bachau, where it emerges on the coast-line. It 

 is in close proximity to the outcrop of basic lava-flows, some of 

 which may have been at or near the surface at the time when it 

 was deposited around them. There is, however, much evidence of 

 faulting, and as no direct junction can be seen, these exposures need 

 not be further described. 



The conglomerate is next seen on the coast at Maen Bachau, 

 south of Castell, a spot readily recognizable, since this rock here 

 forms the bridge of a conspicuous natural arch. The under surface 

 of the bridge is a line of slip, the fault-line being indicated by 

 quartz-spar. But the slip has taken place in such a way as to 

 leave some red sandy Pebidian adherent on the northern side to the 

 under surface of the conglomerate. These beds show at this spot 

 some signs of ending off against and being washed in with the 

 conglomerate. Beneath the fault, which makes an angle of about 

 45° with the vertical, and is probably of no great magnitude, the 

 red Pebidians are seen ending off against the fault-face and resting 

 on an uneven surface of basic igneous rock. Associated with the 

 red beds are dark green tuffs with abundant small, black or, rather, 

 very deep red specks. 



To the north of the arch red Cambrian Cacrfai beds form the 



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