﻿Yol. 66.] GEOLOGY OF THE DISTEICT ABOUND LLANSAWEL. 403 



Birkhill age, and this suggested to us that in the ground which we 

 had traversed there must be a great deal of repetition in the highest 

 Hartfell or in the lowest Birkhill Beds (or in both). We therefore 

 thought it desirable to change our plans, and devote our energies 

 to the establishment of a succession in the Silurian rocks, rather 

 than to the discovery of a junction between them and rocks of 

 Bala age. With this end in view we made Llansawel our centre, 

 and now offer these notes as the result of our researches. 



II. Historical Review. 



Yery little has been written on the geology of this ' most con- 

 torted and perplexing country/ as Sedgwick has called it. The 

 Geological Survey Memoir on North Wales does not give more than 

 the briefest reference to the district in question, and the only papers 

 of real importance are two written by Sedgwick. In the first, 

 entitled ' On the Classification of the Fossiliferous Slates of North 

 Wales, &c.' * he describes very briefly a traverse from Aber Aeron 

 through Lampeter and Pumpsaint by the old road to Llandovery. 

 He thus touched the north of our district, and described the rocks 

 as ' a long series of contorted slates and grits ' (op. cit. p. 154). 

 The traverse is admittedly only a general one, and no definite 

 localities are given ; so this paper is not as important, from our 

 point of view, as the last of a set of three published eight years 

 later, dealing with the base of the Llandovery.- Under the heading 

 1 Conglomerates, Slates, & Sandstones of Dol Fan, &c.' (p. 480), he 

 describes in general terms the rocks composing a wide stretch of 

 country, extending from the south-west of Builth to the 



' high rugged plateau near the watershed of the Cothi and the Towy. . . . 

 [These form] a large and ill-defined group of slates and sandstones, sometimes 

 passing into a coarse conglomerate. . . . This group is generally contorted 

 and forming saddles with sides of high inclination ; the conglomerates are not 

 continuous, but breaking oiF and reappearing ' {pp. cit. p. 480j. 



These furnished only one fossil, a specimen of Euomphalus tri- 

 cinctus. 



Later in 1846 he took another traverse, from Llandovery to 

 Pumpsaint, crossing similar rocks farther south, and from Bwlch 

 Trebanau, 4 miles north-west of Llandovery, he records the fol- 

 lowing fossils : — 



Eucrinite stems. Leptmna sericea. 



Favosites. Orthis elegantula. 



Turbhiolopsis. Atrypa crassa. 



Found on a sub- f Euomphalus tricinctus. Calymene. 

 sequent visit. \ Euomphalus triporcatus. 



1 Quart. Journ. Geol. Soc. vol. iii (1847) pp. 133-64. 



2 A. Sedgwick, 'On the Mayhill Sandstone & the Palaiozoic System of 

 England ' Phil. Mag. ser. 4, vol. viii (1854) p. 472. 



