326 Geological Society : — - 



Man, has studied the coast-section in the Carboniferous volcanic 

 series between Castleton Bay and Poolvash, with the result 

 that he has discovered evidence that the strata have undergone 

 much deformation in pre-Triassic times. In the western part of 

 the outcrop the volcanic material consists almost wholly of tuff, 

 in places bedded and fossiliferous ; in the eastern part exists a 

 chaotic mass of coarse and fine fragmental volcanic material, tra- 

 versed by ridges of basaltic rock and containing entangled patches 

 of dark limestone. The author now considers that the larger 

 3 en tides and most of the smaller blocks of limestone have been 

 torn up from the underlying limestone-floor during a sliding forward 

 or overthrusting of the volcanic series upon it. Such blocks do not 

 contain ashy material, though patches of truly interbedded, ashy 

 limestone are probably also present. The sections at Scarlet Point, 

 Poolvash, and between Cromwell's Walk and Close-ny-Chollagh 

 Point are described and figured. Strips of limestone are found to 

 shoot steeply upward and become wedged in between the blocks 

 in the agglomerate ; they give indications of sliding and disturbance, 

 and their outer surfaces are indurated and chert-like. The ash, 

 which usually rests on black argillaceous limestone-flags, in places 

 appears to come into juxtaposition with a somewhat lower horizon, 

 crushed, platy material intervening between the two. Steep domes 

 of the limestone break into sharp crests, which shoot up into the 

 ash and are bent over towards the north ; and between the crests 

 small ragged strips of limestone are entangled among the tuff. 

 Bands of vesicular basalt are bent and shattered. A dyke-like mass 

 has had a segment sliced off and thrust forward among the agglo- 

 merate, so that its flow-lines of vesicles are sharply truncated along 

 the fractured edge, which is often notched and filled in with ash as 

 though lumps had been torn out of it. The composition of the 

 included masses is influenced by the neighbourhood of the rocks 

 in situ, being calcareous near limestone, and basaltic near the basalt- 

 masses. 



The phenomena may be explained as the effects of earth-movement 

 on a group of rocks consisting of limestone passing up into tuff, 

 interbedded with lava-flows, and possibly traversed by sills or 

 dykes of basaltic rock. The results of the disturbance appear to 

 be limited vertically and horizontally, and to have been determined 

 by the differential resistance of the component rocks. Analogous 

 features occur in the Borrowdale Volcanic Series and in the Silurian 

 volcanic rocks of Portraine. 



2. 'The Zonal Classification of the Wenlock Shales of the Welsh 

 Borderland.' By Miss Gertrude L. Elles. 



This paper deals with the Wenlock rocks of Builth, the Long 

 Mountain, and the Dee Valley, and establishes the following 

 sequence in these districts : — 



