Vol. 59.] AN EXPERIMENT IN MOUNTAIN-BUILDING. 355 



a great extent, represent the conditions prevailing on the earth's 

 surface at different localities and periods. 



If these researches were being carried out by himself, he would 

 use a roughened sheet of rubber attached to a ring, stretched over 

 the top of a cylinder, and, after being charged with the materials of 

 the experiment, allowed to contract. In fact, the arrangement would 

 be similar to that used for stretching parchment-drumheads. He 

 cordially thanked the Author for reviving a question that had of 

 late been neglected, but which would be likely to afford much 

 interesting information. 



He would not terminate without warning experimenters that the 

 lower part of the earth's crust may be far more plastic from heat 

 than had been allowed for in earlier experiments, which would 

 explain the great crumpling of the deeper parts of disturbed 

 areas. 



Prof. J. "W. Spencee thought that some of the models showed 

 resemblance to structures produced in the West Indian islands by 

 denudation, and he compared another with a Mexican plateau. 



The Rev. J. F. Blake said that he was much interested by one 

 of the models exhibited, which showed the production of an elevated 

 isolated plateau or ' horst,' about the origin of which there had been 

 much discussion abroad. In attempting to account for one in a 

 particular instance, he had been led to the conclusion that if strata 

 bent into a syncline between two anticlines were afterwards bent 

 in a direction at right angles, so that a new anticline crossed the 

 old syncline, such a form of ground would result, and he was glad, 

 therefore, to see this conclusion experimentally confirmed when the 

 conditions happened to be suitable. 



Mr. Whttaker said, in regard to the materials used in the 

 experiments, that cloth was excellent for folding only ; but, to show 

 fracture as well, some other material would have to be used. He 

 suggested also the application of a slight upward pressure, as well 

 as lateral pressures. He pointed out that in one set of the casts 

 the centre was a hill, and that in the other set it was a hollow. 



Mr. H. W. Monckton referred to the folded rock now seen at 

 the surface of the ground, and said that he would much like to have 

 some idea as to the amount of strata which had been removed from 

 above the folded rock since the folding took place. The Author's 

 experiments threw light on this question, and seemed to suggest 

 that although folds might be produced near the surface, the more 

 marked folding was produced by pressure at some depth, though 

 perhaps not at so great a depth as was at one time supposed. 



Dr. J. W. Evans suggested that the experiments might be 

 repeated with a local load on some part of the surface, so as to 

 imitate the effects on folding of the accumulation of sedimentary 

 strata on the flanks of a mountain -chain. 



The Authoe expressed his thanks for the complimentary remarks, 

 and the valuable suggestions, which had been made. 



Q. J. G. S. No. 235. 2 c 



