Geology of the District around Llansctwel. 1009 



10 miles to the sea, formed extensive fields of both slaggy and 

 cindery lava (pahoehoe and a a), rilled up a valley to a depth in 

 some places of probably 400 feet, and devastated some of the most 

 fertile land in the island. The crater contains a lake, or rather 

 river, of incandescent lava, so fluid that it beats in waves on the 

 walls, rises in fountains of liquid basalt, and flows with the velocity 

 of a cataract into a gulf or tunnel at one end of the crater. It then 

 runs underground along a channel or channels in the new lava-field 

 until it reaches the sea, into which it flows, and causes explosions 

 attended with the discharge of showers of sand and fragments of 

 hot lava, and the emission of vast clouds of steam. 



The many resemblances to, and few differences from, the volcano 

 of Kilauea are discussed. 



^. ' Notes on the Geology of the District around Llansawel 

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

 Slater, B.A. 



In this paper the authors deal with the stratigraphy and 

 geological structure of a small area some 9 miles to the west of 

 Llandovery, and to the north of Llandeilo. In a brief introduction 

 the reasons for the selection of this region are mentioned, and the 

 work of previous observers is touched upon. 



The rocks consist of a varied series of sediments, including a 

 coarse conglomerate, grits, shales, and tough blue mudstones ; 

 cleavage is almost everywhere intense. 



The beds fall naturally into three divisions, as follows : — 



f O 3. Pengelli Shales (Gala fauna). 

 C. Llansawel Group. < C 2. Zone of Monograptiis communis. 



I O 1. Clyn March or ct/phus Grits and Shales. 



C B 2. Llathige Shales and Mudstones. Zone of 



B. Caio Gro- r J ^ , Mesograptus modesties. 



-d 1. l J enn-y-ddinas Grits and Shon .Nicholas Con- 



\_ glomerates. 



A. Belli Tew Group ..". Beili Tew Grits and Shales. 



The stratigraphical relationships are seen most clearly in the 

 highest, group (C), which is therefore dealt with first. The beds 

 here follow each other in perfectly regular succession, with a 

 uniform strike of E. 30° N. The basal beds, with a fauna 

 belonging to the zone of Monograptiis cypJius, form a well-marked 

 ridge across country, and Lpper Birkhill and Gala Beds follow to 

 the north-west. 



The second group (B) occupies a wide tract to the east of the 

 Llansawel Group. The coarse basal deposits, and the characteristic 

 shales and mudstones, are described from many localities. 



The lowest group (A) has its greatest development on the south 

 of Llansawel. 



The structure in the eastern part of the district shows many 

 points of interest, and is very much more complicated than in the 

 west. The repeated outcrops of the conglomerate in the hilly 

 region around Shon Nicholas are described in detail, and these give 

 the clue to the structure. 



The paper concludes with a general summary and a brief com- 

 parison of this district with those of Rhayader and Pont Erwvd. 



