Reports & Proceedings — Geologists Association. 381 



magraatic pressure is necessary to account for the phenomena 

 observed, and that molten magma may exert even more force than 

 admitted by Gilbert in his laccolithic theory, though not so much 

 as formerlv supposed by von Buch and his followers. 



R. H. R. 



REPORTS AND PROCEEDINGS. 



Geologists' Association. 

 9th June, 1922. 



" The Liassic Rocks of Glamorgan." By A. E. Trueman, D.Sc, 

 F.G.S., University College of Swansea. 



The Liassic rocks of Glamorgan occur in several small outliers 

 near Cardiff and in a broad tract stretching between Bridgend and 

 Cosvbridge, and southwards to the sea. This area is known as the 

 Vale of Glamorgan. In a previous communication the Liassic 

 outliers near Cardiff were described {Proc. Geol. Assoc, xxxi, 1920, 

 p. 93). In the present paper an account is given of the zonal 

 succession in the larger area ; only the lowest zones of the Lower 

 Lias are represented [jjlanorbis-semicostatus), but these are unusually 

 thick (350 feet) and several subdivisions are recognized. Particular 

 attentiot) is drawn to the gryphaeate lamellibranchs of these zones 

 and to their use in correlation. 



In the west of the area the Lias is often of littoral character ; the 

 littoral deposits accumulated near the shores of several small islands, 

 mainly of Carboniferous Limestone. These deposits are best exposed 

 in the cliffs near Southerndown and Dunraven. The relations of 

 the littoral deposits to the normal Lias limestones and shales are 

 discussed and consideration is given to the physical conditions under 

 which the rocks were laid down. 



The paper includes j^etrological notes on the limestones and 

 conglomerates, and notes on some of the ammonites. 



" The Recession of the Chalk Escarpment and the development 

 of Valleys in the Chalk between the Mole and the Darenth." Bv 

 C. C. Fagg, F.G.S. 



Contrast in altitude and features of Chalk area east and west of 

 the Brighton Road. Gaps and passes in the North Downs. Some 

 significant sections. The water-table in the Chalk. Springs and 

 Bourneflows. The Gault outcrop as the decisive factor. Its former 

 extension southward and upward. -Mole Gap and Kenley Valley 

 becoming dry. Recent landmarks in recession of escarpment — 

 Limpsfield Gravel — (500 feet, Acheulian). Passes at Merstham, 

 Godstone, and Pebble-Combe. Relation of these to fiuviatile 

 erosion of " Dry " valleys. Valleys not all of same age. Variety 

 of stones on the Chalk Plateau and their significance. Position of 

 Tertiary escarpment at Wonns Heath and Woodmansterne at close 

 of Pliocene. Possible evidence of present flora of the district. 



Critical review of other hypotheses for formation of Chalk Valleys. 



