818 Geological Society. 



March 22nd.— J. E. Marr, Sc.D., F.R.S., President, 

 in the Chair. 



The following communications were read : — 



1. ' An Experiment in Mountain-Building : Part II.' By the 

 Right Hon. the Lord Avebury, P.C., F.R.S., P.S.A., F.G.S. 



In this paper some experiments are described, which were 

 conducted by an apparatus by means of which pressures could 

 be applied in two directions at right angles to one another, a 

 space of 2 feet square being reduced to one 22 inches square. 

 In the first series, plastic materials such as cloth and thin oil- 

 cloth were used, with layers of sand between them. Two main 

 folds crossing at right angles were formed, the upper one shifted over 

 the lower. The use of two layers of linoleum produced a different 

 type of folding, and the lower layers of the linoleum were broken 

 along the principal ridges. In the second series, a layer of plaster 

 was introduced : this was found to be fractured, tilted up into a 

 1 writing-desk ' form, and forced irregularly into the sandy layers. 

 Overthrusts were thus produced, so that in some cases a boring 

 would have passed through two or even four layers of the rigid 

 substance. In other cases, the edges of the primary fracture broke 

 off more or less regularly, and the detached pieces were pushed up, 

 assuming gradually a very steep angle. The remainder of the edges 

 of the plate of plaster, having now room, were able to approach 

 each other. Pliable material above the plaster was thrown into 

 one or a few extensive folds, while that beneath assumed a greater 

 number of small folds. 



2. ' The Rhsetic Rocks of Monmouthshire.' By Linsdall 

 Richardson, F.G.S. 



The Rhaetic rocks occur only in the neighbourhood of Newport ; 

 and the present paper describes three new sections and four new 

 exposures. They are the following : — Goldcliff, Bishton, Llan- 

 martin. Llanwern, Milton, Bishpool, and Lis-Werry. Measured 

 sections are given at each locality, that at Goldcliff being especially 

 full in the middle portion of the series, because, when visited by 

 the author, it was exposed in consequence of a breach in the 

 sea-wall. The plane of separation between the ' Tea-Green Marls ' 

 (Keuper) and the Black Shales of the Rhaetic is very definite, and is 

 not infrequently accompanied by an inch or two of conglomerate. 

 The Rhaetic ocean appears to have spread with comparative rapidity 

 over the flats of the ' Tea-Green Marl ' in this neighbourhood. 

 The most complete sequence from Keuper to Rhaetic is around 

 Cardiff, where the ' Sully Beds ' (Etheridge's « Grey Marls ' : not the 

 * Tea-Green Marls,' which belong to the Keuper) constitute transition- 

 beds, formed where deposition proceeded continuously. Farther 

 north the 'Black Shales' overstep on to lower and lower portions 

 of the ' Tea-Green Marls.' A non-sequence appears to occur at 

 the base of the Paper-Shales at Goldcliff, where the upper surface 

 of the Cotham-Marble-cquivalent is conspicuously waterworn. 



