Tol. 52.] GEOLOGY OF THE NEIGHBOURHOOD OF CARMARTHEN. 527 



ments, without any clear face. This appearance is very character- 

 istic of the beds whenever they occur in a weathered condition. 

 The fossils obtained were Bellerophon, Ampyx, Cahjmene parvi- 

 frons?, Salt., C. parvifrons, var. Murchisoni, Salt., C. Tristanit, 

 Brongn., distorted fragments of Asaphid trilobites. 



(ii.) Swansea Road Streams. — From the sloping ground which 

 bounds the southern side of Swansea Road two small streams flow 

 northwards to join the Towy. In the lower part of one of these 

 streams we have the D. 6z/icZws-shales, but higher up and apparently 

 dipping under these are mudstones which closely resemble those of 

 Nant Pwntan in colour and hardness. We found here Cahjmene 

 parvifrons, var. Murchisoni, Salt., Ogygia marginata, Orthoceras, and 

 a small Asaphus, sp., Salter ; an exposure in the second streamlet 

 yielded a Calymene. 



In the banks of the steep lane leading to Cilwaunydd Farm were 

 weathered shales containing Bellerophon, Calymene parvifrons, var. 

 Murchisoni, Salt., and Ogygia marginata. 



Totally distinct from these mudstones, and without a fossil in 

 •common with them, are the shales of Hafod-wen spring on the 

 western side of the River Towy. These beds contain a graptolite 

 fauna of Arenig age, but lithologically they resemble the Llanvirn 

 Beds to be next described. We obtained here Didymograptus 

 nitidus, Hall, D. ? constrictus, Hall, D. ? Murchisoni, Beck, Dictyo- 

 cjraptus, sp., JEglina binodosa, and ostracoda. 



3. Didymograptus bifidus-he&s (Llanvirn) . 



These beds consist in some parts of shales alone, in others we 

 have alternating bands of light-grey shales and grey grits, weathering 

 yellow. The grits, which generally are jointed, and often veiued 

 with quartz, vary in thickness from a few inches to several feet ; 

 the shales occur in bands of 6 inches or less. The alternating 

 grit- and shale-bands form a well-marked ridge of hills extending 

 for a considerable distance along the southern side of the Pembroke 

 and Tenby Railway. The beds are almost vertical, but have a general 

 northerly dip on the northern side. Five quarries are cut out on the 

 hillsides, those of Ystrad, Llanllwch, Wernddu, Nant-yr-hebog, and 

 Pen Plas. In the last-named a thicker series of shales is seen just 

 outside the quarry, dipping over the grit-beds, and here Phacops 

 llanvirnensis, Hicks, was found. At Wernddu we obtained Didy- 

 mograptus indentus, Hall ; near Llanllwch and in Ystrad quarry 

 D. bifidus, Hall. North and south of this ridge the beds consist of 

 shales only ; these are of a light-grey colour, fairly soft and well 

 cleaved. South of the ridge, at Ystrad Isaf and Hafod-wen lane, 

 we found Didymograptus bifidus, Hall, D. indentus, Hall, and Diplo- 

 graptus dentatus, Brongn. North of the railway in Trebersed 

 stream a crushed graptolite of the D. patulus-grou]) and a fragment 

 of an eye of JEglina were obtained ; at Castell-y-gaer a portion of a 

 Didymograptus, sp., and of an eye of <sEglina ; farther east, near 

 Trevaughan Hill, we found Didymograptus indentus, Hall, and 

 Diplograptus dentatus, Brongn. 



