264 TKOF. C. LLOYD MORGAN ON THE PEBIDIAN 



doubted Dimetian some distance to the left of the fault-line as drawn 

 by Dr. Hicks in his figure (Q. J. G. S. xl. fig. 13, p. 540). 



d. In the Allan Valley at Forth Clais. — I have no new facts to 

 bring forward with regard to this locality, I could find nothing to 

 convince me of the intrusive nature of the granite in any of the 

 sections exposed. I am not altogether satisfied with Dr. Geikie's 

 mapping of the locality (Q,. J. G. S. xxxix. pi. viii.). There has cer- 

 tainly been some faulting ; but there is no sufficient evidence of the 

 faulted patchwork shown in figure 5 of Dr. Hicks's paper (p. 532). 

 Such a map, apart from its demonstrable errors (e. g. the anticline 

 in the south-west corner, also shown in fig. 5, which has absolutely 

 no existence in nature), is worthless as a guide on the spot, and mis- 

 leading to the student in the study. I spent some time in endeavour- 

 ing to map this locality on the hypothesis of a faulted junction 

 between Dimetian and Cambrian. My complete failure may be due 

 in part to the want of sufficient data ; but it led me to suspect that 

 the Dimetian is intrusive, notwithstanding the absence of any con- 

 vincing evidence at the actual points of contact. 



e. At Ocjof Llesugn. — To this spot the easiest access is by the 

 Cambrian beds a little to the east of the incoming of the Dimetian. 

 Clambering down here by the sucking pool, one skirts the upturned 

 strata — striking I^. 85° W. and nearly vertical, but with a slightly re- 

 versed dip — and descends, at low water, by a cleft opposite the most 

 easterly of the two faults described by Mr. Blake and Dr. Hicks. 

 A long cave occupied by water even at low tide runs here some 

 distance inland. To the west of this is a projecting spur of rock 

 consisting of Cambrian, with massive conglomerate, and apparently 

 some Pebidian. The beds strike about N.E. and show again the 

 inverted dip. There is, to my eye, no indication of the upturning 

 of the strata figured by Dr. Hicks. 



Bej'ond this spur is the more westerly of the two faults, running 

 inland about IN'.N.E. This brings the conglomerate against Dimetian. 

 On the opposite or Dimetian side of the fault, about west of the 

 spur, the conglomerate is again seen. It is in contact below with 

 Dimetian, but there may be a slight slip here. It is overlain, owing 

 to the reversed dip, by red Pebidian. Then follow eight or teu 

 feet of green beds which are separated from the Dimetian by a 

 '' diabase "-dyke. It is difficult here and elsewhere at Ogof Llesugn 

 to separate intrusive diabase from dark green altered Pebidian, and 

 it may be that all the dark material here is " diabase." 



South of this, the western shore of the Ogof Llesugn creeks or 

 bays shows a bewildering confusion of rocks. There are two well- 

 marked masses of conglomerate, much altered and indurated. On 

 the outer face of the more southerly mass (that figured, to me quite 

 incomprehensibly, by Dr. Hicks) there is what appears to be highly 

 altered Cambrian fine-bedded strata. There is a very large amount 

 of much altered Pebidian, red, green, and white. Lastly these 

 Tocks are seamed with " diabase "-dyke material. Here, again, it is 

 difficult to separate this material from Pebidian. But even granting 

 (what I am not prepared to admit) that all the dark green material 



