176 F. D. ADAMS EXPERIMENT IN GEOLOGY 



ous massifs. These beds^, however, were highly inclined. "We are still 

 ignorant/' writes De Sanssure, "by what cause these rocks have been 

 tilted. But it is already an important step among the prodigious quan- 

 tity of vertical strata in the Alps to have found certain examples which 

 we can be perfectly certain were formed in a horizontal position." Then 

 it came to be recognized that these inclined strata were portions of great 

 folds, and later that the mountain system as a whole had originated 

 through the complicated folding of a belt of country. 



It was Sir James Hall who, in 1812, a few years after De Saussure^s 

 death, insisted that the cause of this folding was to be found in great 

 tangential pressure in the earth's crust, developing horizontal thrusts of 

 immense magnitude. In order to demonstrate that such forces could pro- 

 duce the results observed, he constructed a machine in which a series of 

 layers of cloth of different sorts, alternating with stuffs of other kinds, 

 were submitted to great lateral pressure while under a heavy vertical 

 load. Thin layers of clay were in a later series of experiments substituted 

 for the cloth. By these experiments Hall was able to show that folding 

 of the type seen in mountain chains could be developed by such lateral 

 thrusts, and that in his particular experiments the convolutions of the 

 Silurian strata of the Berwickshire coast were reproduced in a striking 

 manner. 



He was followed after a long interval by Cadell, who, in 1888, carried 

 out a series of experiments in which alternating layers of sands of differ- 

 ent colors, clay, and plaster of Paris, resting on a bed of plastic wax, were 

 deformed in a similar manner, with a view more particularly to ascer- 

 taining under what conditions of pressure overthrusts such as those 

 which were being discovered in the highlands of Scotland would be de- 

 veloped.^ 



Among some of the important results which he obtained were the facts 

 that overthrusts did not necessarily originate in the disruption of over- 

 turned folds, but were often produced directly by horizontal thrusts, and 

 that a deep lying overthrust might pass upward into an anticlinal fold 

 and thus never come to be visible as an overthrust at the surface. 



Daubree,^ Pfaff,'^ Meunier.^ Schardt,^ Eeyer,^^ and others carried out 



5 Experimental researches in mountain-building. Trans. Roy. Soc. of Edinburgh, vol. 

 XXXV, 1888, p. 337. 



^ Loc. cit. 



'' Der Mechanismus der Gebirgsbildung. Heidelberg. 1880. 



^ La Geologie Experimentale. Paris. 1899. 



^ fitudes Geol. sur le Pays-d'Enhaut Vaudois — 3' partie, A. Mechanism des Disloca- 

 tions. Bull, de la Soc. Yaudoise des Sciences naturelles, 1884. 



10 Geologische und Geographische Experimente. Leipzig, 1892-1894. 

 Ursachen der Deformationen und Gebirgsbildung. Leipzig, 1892. 



