250 PROP. C. LLOYD MORGAN OX THE PETJIBIAN 



coast-line, and beneath them are green sandy shales. These are 

 separated from Pebidian b}- a quartzose fault-line, broken fault-rock 

 lying on the lower rock-surfixee. The conglomerate is here cut out. 

 The Pebidians show the incoming of sedimentary conditions which 

 is so noteworthy at Ogof Golchfa. The red and green Cambrian 

 beds are invaded by a dyke of basic igneous rock. 



In the little creek immediately to the south of the arch the con- 

 glomerate, here thick, has been thrown back by a little east and 

 west fault, and rests upon the surface of green Pebidian tuff with 

 the dark specks before mentioned. The beds in this creek are a 

 good deal troubled, and the junction is somewhat obscure. I could, 

 however, find no satisfactory evidence of anything like a systematic 

 unconformity. 



The included fragments in the conglomerate are here remarkable, 

 as will be presently noticed. 



In the next creek southward there must be more faulting ; for 

 the green sandy Cambrians are seen striking at the conglomerate. 



The following creek shows the green sandstones (striking jS^. 25° E. 

 and dippiug about 40° seawards) overlying the conglomerate. 



In the next creek there occurs a considerable fault. The northern 

 cliff-face is conglomerate, against which the silky schistose Pebidians 

 with associated porcellanites strike about N. 45° E. It is not difficult 

 to clamber down here. At the base of the conglomerate is a cave 

 (Ogof Goch) following the line of the fault, which runs S. 70° W. 

 The Pebidian in contact with the conglomerate is at first sight a 

 dirty dark-green basic-looking rock. When polished, however, it 

 is seen to be a rich green with lighter veins. I prepared a speci- 

 men for microscopic examination. The following is Mr. Grenville 

 Cole's description of the slide : — " A rock probably composed of 

 ferruginous clayey particles, with lava chips and tuff-fragments, 

 washed into it. The sedimentary part — the clays — seem reduced 

 chemically, and the iron separated, probably as magnetite dust. 

 The whole has undergone squeezing." Although it is probable that 

 the rock has undergone alteration, it is obviously very different 

 from the silky beds and porcellanites on the other side of the dis- 

 placement. But in the cave and so close to the fault the relations 

 of Pebidian to Cambrian at the junction cannot be readily observed. 



So far as I can ascertain, it is to this spot that Dr. Hicks's fig. 14 

 {I. c. p. 542) purports to have reference. I could find nothing here 

 or elsewhere on this coast-line in any way resembling it. The 

 Ogof Goch fault, the effects of which are well marked here and 

 inland, is not noticed by either Dr. Hicks or Dr. Geikie. 



Pebidian strata form the coast-line for about half a mile beyond 

 Ogof Goch until we reach Carn-ar-wig, where another well-marked 

 fault occurs. On the south-western point beyond this bay the 

 last exposures of the conglomerate occur*. Speaking of this locality 

 Professor Blake says : — " Though there is no fault here, all the 

 rocks being laid quite bare, no better proof could be desired, derived 



* These exposures are not mentioned by Dr. Hicks or marked on his map. 



