﻿404 MISS DREW AND MISS SLATER ON THE [Aug. I9IO, 



These were identified in the field by Salter, but unfortunately 

 never reached Cambridge; Sedgwick states, however, that taken 

 together they indicate a group below the Mayhill Sandstone, which 

 is therefore Cambrian (op. cit. p. 481). 



The Bwlch Trebanau Conglomerate falls just outside our area, 

 but we believe it to be identical, and indeed continuous, with our 

 Shon Nicholas Conglomerate. From this we were unfortunate in 

 obtaining no identifiable fossils ; but, in the absence of definite proof 

 to the contrary, we consider it as basal Llandovery. 



Sedgwick then records to the south, intimately associated with 

 the conglomerates, but on a lower geological horizon, 



' a very great development of rather earthy slates, and of arenaceous flag- 

 stones, sometimes coarse, and almost deserving the name of conglomerates : in 

 •which case they are often ferruginous ' (op. cit. p. 481). 



Fossils were obtained from many localities, and these gave a very 

 characteristic Upper Bala horizon. These rocks we believe to be 

 our Beili Tew Group. 



III. General Geology. 



The district is a hilly one, for the ground is everywhere as much 

 as 300 feet above sea-level, rises often to 1000 feet, and sometimes 

 to 1400 feet. One of the most noticeable features is the well- 

 marked north-easterly and south-westerly trend of the hills. These 

 run in parallel ridges broken by transverse valleys, containing small 

 streams, flowing into the Cothi. This tributary of the Towy drains 

 the whole district, and has carved out for itself a wide and flat- 

 bottomed valley, filled with drift and alluvium. From Pumpsaint 

 for about 3 miles the river flows in a southerly direction ; it then 

 bends round south-westwards, flowing parallel to the trend of the 

 hills. (See map, PL XXIX.) 



On the north-west the ground rises gradually to the main water- 

 shed between the Teifi and the Towy basins, but on the east the 

 ridges are more broken up into isolated knobby crests. 



The area is on the whole poor in rock-exposures, as the greater 

 part consists of rich pasture and arable land. The underlying rock 

 is therefore for the most part seen only in road-sections, in small 

 quarries, in broken ground on the hill-tops, and in the stream- 

 section of the Gorlech, for all the other streams flow in drift or 

 alluvium. 



In the area under consideration the rocks consist of a varied series 

 of sediments with a remarkably uniform strike of E. 30° N. They 

 include a coarse conglomerate, grits, shales, and hard blue mudstones. 

 The last-named are the most prevalent, but it is a striking feature 

 of the whole series that numerous gritty bands of varying thickness 

 occur throughout. As we go north from Llandeilo, cleavage, which 

 is hardly noticeable there, becomes rapidly more apparent, and all 

 around Llansawel the rocks have suffered intensely, so that in some 

 places they are reduced to splintery fragments, with no trace of 



