﻿356 AN EXPEEIMENT IN MOUNTAIN-BUILDING. [May I905, 



them : for instance, it was doubtful whether we could ever get 

 sufficient pressure to imitate exactly that flow of solids of which 

 there was evidence among the rocks. 



The initial experiments of Eavre were simple, but others, as Cadell 

 and Willis, had made more elaborate experiments, and the Author 

 had introduced further complications. 



The paper which had just been read was a continuation of one 

 previously presented to the Society by the Author, and the President 

 hoped that Lord Avebury would continue his interesting experiments 

 and bring further results before the Society. 



Dr. Blanfoed said he thought that the Society were greatly 

 indebted to the Author for a most interesting series of experiments. 

 He was particularly impressed by the crossed faults produced in the 

 layer of plaster, as this probably showed the way in which lateral 

 pressure might act on a rigid bed intercalated among more flexible 

 strata. The form of the surfaces produced naturally differed from 

 that of the usual superficial features of the land, because of the 

 absence of the erosive action of denudation. 



Prof. Garwood asked the Author whether sections cut through 

 the models showed the formation of cavities such as might induce 

 the intrusion of igneous rocks in Nature, and such as seemed to 

 have taken place in mountain-ranges like the Eastern Himalaya. 



Mr. Lamplugh remarked on the close resemblance of the plica- 

 tions on the surface of the models which contained linoleum, to 

 the corrugations sometimes shown by compressed gritty flags in the 

 Isle of Man and at Bray Head in Ireland. 



Mr. Steahan thought that the imitation of forms of surface 

 produced by denudation, by the surfaces of the models as produced 

 by folding, was apt to mislead, and suggested that a truer com- 

 parison with Nature might be obtained by planing off the surfaces 

 of the casts to a level, and developing valleys and escarpments by 

 erosion. The model showing two intersecting overthrusts was 

 especially instructive. Though contemporaneous with it, one 

 overthrust clearly broke through, and displaced the other. More- 

 over, the one that was broken through was overthrust from opposite 

 directions in its two halves, in this respect resembling belts of 

 overthrusting and compression in Nature, which, unlike normal 

 faults, were apt to change their throw. 



It would be interesting to see a reproduction of a structure that he 

 had recently observed in Pembrokeshire. There a gentle anticline 

 was accompanied by a multitude of small overthrusts. Without ex- 

 ception, the overthrusting was from the south on the south side, and 

 from the north on the north side of the anticline. Even in the few 

 yards of nearly-level strata in the crest, four or five little over- 

 thrusts strictly followed this rule. He joined previous speakers 

 in hoping that these interesting experiments would be continued. 



Mr. Whitaxee enquired what was the amount of pressure 

 exerted on the top during the whole of the experiments. 



The Authoe thanked the President, and the other Fellows of the 

 Society who had spoken, for their kind remarks. It was said that 



