'526 MISS CROSFIELD AND MISS SKEAT ON THE [Aug. 1 896, 



greatly resembles the Tremadoc Slates, but, on the whole, is harder, 

 and not interstratified with grits or sandstones. The shales in the 

 lane dip south, and thus pass under the older Tremadoc Beds. We 

 find this inversion of the normal succession in all the strata on the 

 southern side of what we may term the Mount Pleasant and Tstrad 

 ridge. The fossils obtained here were mainly trilobites, but a few 

 specimens of FhyUograptus, sp., were also found. The list is as 

 follows : — Ampyoc, sp., Ogygia marginata, Ctenodonta, Phyllograptus, 

 sp., cf. angnstifolius, Hall. At Pen-y-banc, about -J- mile eastward, 

 the same species of Ogygia and a Lingula were obtained. 



Confirmatory Sections. 



The small stream above Pwntan House, west of the river Towy, 

 lias cut its way through similar mudstones of a rather lighter colour. 

 In this rock the bedding-planes are tolerably far apart, and the 

 intervening rock breaks with difficulty. The fossils are abundant 

 and well preserved, but consist entirely of Ogygia marginata and of 

 a few specimens of Ctenodonta. East of the Towy similar mud- 

 stones may be seen in the brook which passes under the road 

 •close to Carmarthen Junction, but only a few distorted portions of 

 Ogygia marginata were obtained. 



At Allt Pen-y-coed, 2 miles nearly due east of Carmarthen 

 Junction, the mudstones are exposed in a fine deep gorge ; the beds 

 are not very fossiliferous, but yielded a head and tail of Ogygia, sp., 

 cf. Selwynii, Salt. 



In the banks of the Nant-y-Caws, on the same strike, is a great 

 thickness of shales lithologically similar to those of Glan Pibwr, but 

 containing, both in the upper and lower parts of the gorge, bands 

 of grit and some conglomerates. As the dip varies from 35° N., not 

 tar from the bridge in the lower part, to 55° S. 30° E. at the water- 

 fall, where the junction with the Old fled Sandstone occurs, we have 

 probably here a small subsidiary anticline. These shales are very 

 nnfossiliferous, and only yielded Orthoceras sericeum and Conularia. 

 We have placed these beds provisionally with the Arenig Series, but 

 whether they do not belong rather to the Tremadoc Slates is open 

 to question. 



Lying to the north of the beds which we have just described 

 are others ot similar lithological and palasontological characters, 

 differing only in the fact that they contain in addition Calymene 

 joarvifrons, var. Murchisoni, Salt. 



The chief localities where the beds containing Calymene crop out 

 are (i.) the Roman Road. — This exposure extends along both sides 

 of the deep lane of this name in the Pensarn district of Carmarthen. 

 The beds are shaly throughout, but vary in character in different 

 parts of the road. In the hard, rather flaggy beds, about halfway 

 up the lane many fossils were found in a very fragmentary con- 

 dition, this being partly due to the fact that the bedding is almost 

 at right angles to the cleavage. Higher up the road the shales are 

 hopeless for purposes of search, being crushed and weathered to 

 such an extent that they break always into long billet-shaped frag- 



