604 MR. D. C. EVANS ON THE ORDOVICIAN [NOV. I906, 



of recognizing the beds in the absence of fossils — and these are 

 generally very scarce. Without some such guide, it would be 

 often impossible to distinguish these beds from others higher in the 

 succession. 



The grits and conglomerates west of the Fenni vary considerably 

 in thickness, colour, and texture. All the evidence available points 

 to their being a local development in the 2 y etragrajjtus-Beds, and 

 there are strong reasons for believing that their real is much greater 

 than their apparent extent, for they have been subjected to much 

 folding and faulting. One very noticeable feature which they 

 present is that they are exposed on the higher ground much more 

 extensively than in the valleys — capping the hills in gentle folds 

 which do not often reach the lower ground. 



& j 



(1) TheLowest Shale s. — The lith ological character of the very 

 lowest beds is that of the usual Tetragraptvs-Shales of the district, 

 but they contain fossils very sparingly, so sparingly that it is 

 difficult to fix their age definitely. In the absence of sufficient 

 proofs to the contrary, they are here placed at the base of the 

 Middle Arenig — or Didymograptus-extensus zone. 



These shales are well and abundantly exposed in the neighbour- 

 hood of Whitland Abbey. They are seen all along the road leading 

 from that place to Pass-by Cottages on the north-west. They 

 contain very few fossils here, and those that do occur are in a 

 very fragmentary state. Among others are trilobites — probably 

 JEglina, a Palcearca, and an Orthoceras. Similar beds are seen at 

 Cwmfelin-boeth, near the small bridge on the Whitland road. 

 These have yielded an Orthoceras, a Trinndeus, and some small 

 fragments of an unidentifiable graptolite. The blue-black mudstones 

 in the quarry on the roadside a short distance farther south, 

 undoubtedly belong to the same series. Some trilobite-fragments 

 have been collected here, but were so badly distorted that only with 

 hesitation could they be assigned to the genus JEglina. 



These beds also come to the surface at frequent intervals in the 

 valley of the Gronw, and here they have yielded some extensiform 

 graptolites a little to the north of the Old Cottage, north-east of 

 Llwyngwydd. The graptolites here are associated with Orthoceras 

 sp., Caryocai'is-t&ih, and Orthis Carausii, Salt. A few graptolite- 

 fragments were collected also from the small section immediately 

 south of Penyglog, and were associated with Mglina, Theca, and 

 Orthoceras. 



Certain shales are abundantly exposed near Pantgwyn and 

 Aberdauddwr in the Nantclomendy valley. Some of them un- 

 doubtedly belong to this horizon, but whether those occurring in 

 Aberdauddwr farmyard are of this age may be questioned. As 

 regards texture and colour, these are much like the Upper Tetra- 

 gra<ptus-Beds ; but graptolites, though present, are very scarce and 

 fragmentary. Other fossils collected here are : — JEglina sp., Tri- 

 nucleus sp., Agnosias cf. M'Coyii, Salt., Beyrichia, Orthis cf. 

 Menapue, Hicks, and Lingula sp. 



