G32 Geolojical Society: — 



and ]ion-scqucntially, upon the Upper Freestone, whereas obser- 

 vation shows the intervention of at least the Buchmani-Qnt, part 

 of Avhich thins out from 4 inches at the north-en stern end, to 

 nothing at the other end of the quairy, which is in the direction of 

 the anticlinal axis. The error is not one of fact but of inference, 

 and the present evidence rectifies portions of those limits wliich 

 were drawn theoretically. A section near the ' Air-Balloon' Inn, 

 on the road from Birdlip to Cheltenham, shows the Lower Trigonia- 

 (/rit covered by Buckmani-Gnt and underlain by the Upper Free- 

 stone. There is only one section where the Upper Trigonia-Grit is 

 seen to rest directly upon the Lower l^rigonia-GTit, the latter being 

 only 3 feet 2 inches thick. The causes producing the Bajocian 

 denudation appear to have been forces so acting as to effect a repe- 

 tition of flexure along old lines of weakness ( Aalenian) ; and thus in 

 the J^irdlip area an anticline may be again located, but the elevation 

 was this time much greater : indeed, the level of the Aalenian denu- 

 dation was passed by the Bajocian. Other sections near Brimpsfield 

 and in Cranham Wood are given in connection with the location of 

 the anticlinal axis. The exact location of the anticlines and 

 syiK'lines of the Inferior- Oolite rocks in the Cotteswolds, where 

 sections are numerous, may afford some important working hypo- 

 thesis for unravelling the structure of the Yale of Gloucester, where 

 excavations are few. 



3. ' Description of a Species of Heterasircea from the Lower 

 Ehaetic of Gloucestershire.' By Eobert P. Tomes, Esq., P.G.S. 



May 27th.— Edwin Tulley Xewton, Esq., F.Il.S., 

 Vice-President, in the Chair. 



The following communications were read : — 

 1. 'An Experiment in Mountain-Building.' Bv the Eight Hon. 

 the Lord Avebury, P.C., F.E.S., F.G.S. 



Yarious observers have endeavoured to throw light on the origin 

 of mountains by compressing pieces of cloth, etc. In these cases, 

 however, the pressure was only in one direction. The author 

 wished to obtain a method of obtaining compression in two 

 directions at right angles to one another; and, accordingly, he had 

 an apparatus constructed, consisting of four beams of wood, which 

 could be approximated by means of screw^s. In the space, 2 feet 

 across and 9 inches in depth, were placed pieces of carpet-baize 

 and layers of sand, each about 1^ inches deep. The beams were 

 then caused to approach one another until the sand rose in the 

 centre into contact with the glass cover, against which it was 

 flattened out. Casts were made of the surfaces of the different 

 baize-layers, and it was found that in the lower layers the ridges 

 were narrower, shorter, more precipitous, and more broken up, 

 than in the higher layers. A second series of casts was exhibited, 

 with the sand and baize having been arranged as before, but with 

 the weight placed on one side. The ridges followed the edges, 

 though not closely, leaving a central hollow. There was a difference 



