510 MR. 0. T. JONES ON THE HAETEELL-VALENTIAN [JS~OV. 1909, 



yielded Monograptus resurgens only about the middle of the section 

 (F. 46). The beds are folded into an anticline, and are followed by 

 a considerable thickness of hard, compact, blue mudstones. At the 

 foot of the great crags which rise to the east of the gully I obtained 

 the following graptolites (F. 47) : — Rastrites tinned, Monograptus 

 becki, M. marri, M. nudus, and M. resurgens. This assemblage is 

 not unlike that at the western end of the valley, and from the 

 nature of the folding it does not seem improbable that the rocks 

 at these two localities are nearly on the same horizon. 



About a quarter of a mile to the east is another imposing line 

 of crags, the debris from which tails for a long way down the 

 slope. I could find no fossils in situ ; but, by searching carefully 

 in the debris, Dr. Herbert Lapworth and I obtained a fairly good 

 collection, consisting of the following species (F. 48) : — Monograptus 

 crassus, M. cf. exiguus (v.c.), 1 M. galaensis, M. cf. holmi, M. 

 marri (?), M. nudus, M. tortilis (?), and a curious large curved 

 Monograptus which I could not identify specifically. 



From this point to the end of the section the south side of the 

 valley presents a succession of rocky crags, alternating with slight 

 depressions or narrow clefts which mark the position of bands of 

 soft shale among the more intractable mudstones. Graptolites may 

 be obtained from all the shaly bands. 



South of Blaen Myherin Farm dark-blue thickly-bedded mud- 

 stones, of a smooth soft texture and weathering in orange-yellow 

 and vermilion tints, make their appearance ; they are associated 

 with bands of dark shale, weathering in brighter colours, which 

 yielded graptolites in several places. A thick bed of shale which 

 occurs in a prominent groove in the hillside due south of Blaen- 

 Myherin Farm (F. 49) yielded Monograptus galaensis, M. marri, 

 and a form which approaches most nearly to M. priodon. 



Another bed about 100 feet higher (F. 50) gave Monograptus 

 distans, M. exiguus (c), M. holmi, M. nudus, and M. tortilis ; while 

 another baud about the same vertical distance above it (F. 51) 

 furnished Monograptus exiguus, M. nodifer, M. nudus, M. turri- 

 culatus (a), and Petalograptus palmeus var. tenuis. 



The section practically ends at the cart-road leading from the 

 farm to the peat-grounds on the south, there being only a few 

 scattered exposures of dark-blue mudstones beyond this for a 

 considerable space 



When the western edge of the moorland tract of Cefn Croes is 

 reached, a coarse, grey, speckly felspathic grit makes its appear- 

 ance rather unexpectedly, while the ground is covered in places 

 with its debris. This rock compares better with the coarse grits 

 of Plynlimon than with anything else in the whole succession, and 

 therefore it is important to ascertain its relationship to the great 



i This is probably the form mentioned by Miss E. M. E. Wood (Mrs. Shake- 

 spear) in her paper on ' The Tarannon Series of Tarannon ' Quart. Journ. 

 Geol. Soc. vol. lxii (1906) p. 679, footnote. 



