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



16. Notes on the Geology of the District around Llansawel 

 (Carmarthenshire). By Miss Helen Drew, M.A., and 

 Miss Ida L. Slater, B.A. (Communicated by Dr. J. E. Marr, 

 F.R.S., F.G.S. Bead April 13th, 1910.) 



[Plate XXIX — Geological Map.] 



Contents. 



Page 



I. Introduction 402 



II. Historical Keview 403 



III. General Geology 404 



IV. Detailed Description of the Beds 407 



V. -Detailed Structure of the Outcrops of Conglomerate ... 413 



VI. Detailed Structure of Pen-y-ddinas and BancBeili Tew. 414 



VII. General Summary 416 



VIII. Comparison with the Deposits of other British Areas . 416 



I. Introduction. 



In 1906 and 1907 respectively, we were the recipients of the 

 Daniel Pidgeon Fund, and decided to undertake a piece of field- 

 work among the Palseozoic rocks of Wales. 



It was suggested to us that we should make the country north 

 of Llandeilo the seat of our investigations, with the view of dis- 

 covering, if possible, the junction between the rocks of Hartfell 

 and those of Birkhill age. We knew that Lower Birkhill graptolites 

 had been found at Pumpsaint, some 11 miles to the north of Llan- 

 deilo, and we therefore hoped that the intermediate country might 

 furnish sufficient fossil evidence to give us this line of junction. 



With this end in view, we first made our headquarters at 

 Llandeilo, and studied the country north of that investigated by 

 Mr. T. C. Cantrill and Mr. H. H. Thomas. However, we found 

 that the same monotonous series of highly-cleaved unfossiliferous (?) 

 shales, apparently of Upper Hartfell age, continued so persistently 

 to the north as to give us no hope of a graptolitic succession there. 

 While pursuing our way still farther north, in search of some 

 change in the lithology, our attention was attracted by some large 

 slabs of a hard blue mudstone, standing outside a smithy ; on close 

 inspection these showed unmistakable fragments of graptolites, 

 preserved in pyrite. By the help of very vague directions, given 

 in Welsh by the smith, we succeeded, after considerable difficulty, 

 in locating the quarry from which the slabs had been brought. It 

 is situated on the south side of the Llandovery-Lampeter Boad, 

 near a farm known as Bwlch Cefn Sarth, some 9| miles north of 

 Llandeilo, and 4| miles east of the little village of Llansawel. 



The graptolites obtained from this rock proved to be of Lower 



