Vol. 62.] ROCKS OF WESTERN CARMARTHENSHIRE. 619 



The second outcrop is isolated from the first by a belt of newer 

 beds faulted down or folded in. It extends from a point a short 

 distance east of Clyngwynne House to another point a short distance 

 south-west of Cwrtau-bach. Didymograptus bifidus was collected 

 from the following localities: — A well in Clyngwynne field; the 

 road-section at Cross-in; roadside exposures near the Parsonage; 

 Parsonage Quarry ; Common Quarry ; Wern-oleu-fawr ; roadside 

 north of Post-gwyn ; and Cwrtau-bach. 



A diabase-dyke cuts obliquely through the outcrop near Parsonage 

 Farm, and is quarried for road-metal in the Parsonage Quarry. 

 The beds roll about a good deal near Cwrtau-bach, owing no 

 doubt to much faulting in the immediate neighbourhood. On 

 the north the beds pass up normally, except from Wern-y-berni 

 westward, where the succession seems to be broken by a fault — 

 probably a thrust. 



(3) Conclusions. — The occurrence of Didymograptus Muixhi- 

 ■soni var. geminus in certain sections suggests the propriety of 

 separating those beds from the D. -bifidus, and including them in 

 the D -Murchisoni Series ; but certain considerations make that 

 arrangement inconvenient and illogical, so far as the two faunas 

 are represented in this district. 



In the first place, D. Murchisoni var. geminus appears rather low 

 down in the series, associated with a fair number of graptolites — 

 extensiform and others — of true D.-bifidus age ; in the second 

 place, much higher beds have yielded series of fossils of true 

 D.-bifidus facies ; and in the third place, there is in this district a 

 natural well-defined line of demarcation between the D. -Murchisoni 

 Beds and those of D.-bifidus &ge — a line characterized by lithological 

 and faunal conditions, and easily traced wherever the two series 

 occur in normal succession. 



(c) Llanvirn Group : Didymograptus-Murchisoni Beds. 



(1) South of the Anticline. — In the absence of a single 

 •exposure, it is doubtful whether these beds occur at all on the 

 south of the anticline. A few fragments of striped flags, containing 

 isolated stipes of ' forked ' graptolites, have been found in the soil, 

 near a small quarry in Asaphus-tyr annus Limestones north of Lower 

 Court. The general aspect of the specimens suggests Didymograptus- 

 Murchisoni Beds. 



Black mudstones containing crowds of ' forked ? graptolites, 

 associated with great numbers of Siphonotreta micula and a few 

 specimens of Orthoceras, have been dug out of a well at Croft 

 Lodge. These beds, with their fossil contents, bear a striking 

 resemblance to black mudstones underlying and passing up into 

 Asaphus-Limestones near Lan Mills. 



The graptolite-mudstones at Croft Lodge underlie Didymograptus- 

 bifidus Beds, and do not come to the surface anywhere in the 

 neighbourhood — a fact which adds force to the view that there 

 is an extensive overfolding here. 



