﻿418 MISS DREW AND MISS SLATER ON THE [Aug. I9lO v 



rest, the few fossils found in scattered localities have been used 

 as an indication of the zonal horizon, and not for the establish- 

 ment of the sequence of graptolites ; where there is an apparent 

 anomaly in the assemblage of forms, as at L. 4, at which place 

 Climacograptus tbrnquisti occurs with Glyptograptus jpersculptus, the 

 preservation is so bad that the species is not to be relied upon. 



In conclusion, we wish to express our thanks to those who 

 have so kindly helped us : to Mr. H. H. Thomas, M.A., F.G.S., 

 for very valuable encouragement and advice at the outset ; to 

 Miss G. L. Elles, D.Sc, for the identification of all our graptolites ; 

 and more especially to Prof. 0. T. Jones, M.A., F.G.S., who is 

 really responsible for the existence of this paper, for, without his 

 encouragement and assistance on one or two critical occasions 

 during the progress of the work, we should have been sorely 

 tempted to abandon it in despair, and leave this perplexing 

 district to others more fitted to cope with its problems. 



EXPLANATION OF PLATE XXIX. 



Geological map of the district around Llansawel (Carmarthenshire), on the 

 scale of 2 inches to the mile. 



Discussion. 



Prof. 0. T. Jones congratulated the Authors on the patience and 

 persistence with which they had carried out the investigation of a 

 particularly difficult piece of country. The paper brought out for 

 the first time the extraordinary difference between the facies of 

 the Valentian rocks on opposite sides of the anticline which ranges 

 down the Yale of Towy. On the south-east side is situated the 

 type-area of Llandovery, characterized by ' shelly ' fossils almost 

 exclusively. Very few graptolites have ever been found in that 

 area, but other fossils are abundant at certain horizons. On tile 

 north-west side of the anticlinal axis the Valentian fauna ia 

 almost entirely graptolitic, and no ' shelly ' fossils have been 

 recorded, except from the basal conglomerates. The distance 

 which separates the two facies at the present day is only 8 to 

 10 miles, but must have been greater originally, as the rocks in 

 the intervening space are considerably folded and repeated by 

 strike-faults. Even making allowance for this, however, it is 

 evident that the transition from one facies to the other must have 

 taken place with comparative abruptness. The transitional belt 

 can be traced from this region, both in a north-easterly direction 

 into North Wales and in a south-westerly direction towards Pem- 

 brokeshire. 



Dr. Herbert Lapworth congratulated the Authors on their 

 completion of a very difficult piece of work. He referred to the 

 remarkable fact that, although graptolitic zonal work had been 

 carried on for over thirty years in the Llandovery rocks of Britain,. 



