Vol. 52.] GEOLOGY OF THE NEIGHBORHOOD OF CARMARTHEN. 531 



7. Bala Beds. 



Partly surrounded by shales of Arenig age is a great series of 

 mudstones, grits, sandy flags, sandstones, and conglomerates. These- 

 beds extend from near Mount Pleasant, the residence of Sir Lewis 

 Morris, for more than a mile in an easterly direction, and probably 

 farther. They are bounded on the north by the Arenig Beds of the 

 Roman Road and by the River Towy. On the south they rest on 

 the Arenig Beds of Glan Pibwr and Cilwaunydd. In the centre of 

 the series the beds are perpendicular, as is well seen in the flag- 

 stones and pebble-beds of Bolahaul Quarry, and in the alternating 

 grits and shales in the quarry opposite Mount Pleasant Nurseries. 

 Eossils of Bala age have been found at Pensarn, the Star Inn,. 

 Allt Cystanog, and Erw-wen. Pensarn is classical ground, for in 

 the dark-blue brittle mudstones which recur near the northern 

 end of the deep lane called the Roman Road, Lady Murchison ' 

 found Stygina [Ogygia] Murchisonce, Murch., which was figured 

 with other fossils from the same locality by Sir R. I. Murchison. 

 This appears to be a small isolated patch of Bala Beds, as it occurs 

 between the Arenig Beds of the upper part of the lane and the- 

 Llanvirn Beds to the north. Close to the spot marked ' Spring ' on 

 the 25-inch Ordnance map we obtained ? Homcdonotus, Stygina 

 Murchisonce, Murch., Orihis alata, Sow., and Bellerophon. 



Confirmatory Sections. 



In a lane behind the Star Inn, on the Llandeilo Road, the beds are 

 more flaggy in character; here we obtained Lingula tenuigranulata, 

 L. Icevis, Orthis alata, Sow., and Nucula Icevis. These flags, which 

 lie on the northern slope of the Mount Pleasant ridge, may be 

 traced for a short distance up the hill, and are seen again at 

 Erw-wen, | mile south-east on the southern slope of the hill. 

 Here we found Orthis alata, Sow., 0. calligramma, Dalm., O.fiabcl- 

 lulum, Sow., Lingula, sp., Bellerophon, and Nucula. 



At Allt Cystanog mudstones lithologically similar to those of 

 Pensarn have been turned out of the new lead-mine. Here we 

 collected Lingula tenvigranulata, Orthis alata, and 0. fiabellulum. 



In a quarry opposite Mount Pleasant Nurseries we found a few 

 fragments of Ilolopella. 



IV. Comparison with the Deposits of other Areas. 



1. Tremadoc Slates. 



It is unfortunate that we have not found in these beds a single 

 fossil which is characteristic of the Tremadoc Slates in other parts 

 of Britain. The commonest trilobite that occurs is a new species 

 of Peltura, Milne-Edwards ; but we have also two other Cambrian 

 forms : a Parabolinella closely resembling P. rugosa, Brog., which i;> 



1 ' Silurian System,' pt. ii. pp. 358 & G64, & pi. xxv. figs. 3 a, 36. 



