ME CADELL ON EXPERIMENTAL RESEARCHES IN MOUNTAIN BUILDING. 339 



it was stiff enough to resist much bending, but not too rigid to prevent some interstitial 

 movement throughout the mass. Clay was also used in some cases, usually in associa- 

 tion with less plastic strata. 



The experiments were of three distinct kinds. The first series (A) was designed to 

 explain the behaviour of different types and arrangements of strata when pushed 

 horizontally over an immovable surface. The object of the second series (B) was to 

 ascertain if possible how gently-inclined "thrust-planes" may have originated, and to 

 trace their connection with " fan structure " and other phenomena observed in mountain 

 systems of elevation. The third series (C) was conducted on principles suggested by 

 the experiments of Favke, who placed layers of clay on a stretched india-rubber band, 

 and on allowing it to contract, produced miniature mountain ridges by the wrinkling of 

 the surface of the clay. I extended Favre's experiments by removing the upper layers of 

 the wrinkled clay, and observing the effect of the contraction on the deep-seated portions 

 of the miniature mountain system. 



A. Thrusting over an Immovable Surface. 



The strata were formed in a rectangular box 6 or 8 inches broad and 3 to 5 feet long. 

 One end of the box was movable, and could be pushed in so as to compress longitudinally 

 the strata inside. At the beginning of the experiments, the sliding end piece, which 

 may be called the pressure board, was pushed in, either by hand alone, or if the force 

 required were considerable, with the help of a lever. In the last and most complete 

 series of experiments, the pressure was applied by means of a strong screw running in 

 bearings bolted to the prolonged sole of the box. The sides could be removed at pleasure, 

 when it was desired to examine the section of the distorted strata inside. The figure on 

 the following page gives a general idea of the size and nature of the whole apparatus. 



In proceeding with the experiments, after the pressure board had been pushed in far 

 enough to produce some marked change in the internal structure of the mass, the side of 

 the box was removed, and the vertical section thus exposed was pared along the edge 

 with a sharp knife, to reveal the beds clearly and remove all traces of friction with the 

 wood. If the results were of interest the section was accurately sketched, traced, or in 

 most cases photographed, a measuring tape having previously been attached alongside 

 of the section to show the scale of the operations in feet and inches. 



If it were desired to continue the experiment, the side was replaced, and the pressure 

 board pushed further in, after which the new section was examined and recorded as 

 before. In several of the experiments the process was repeated four or five times to 

 indicate the successive steps in the formation of the ultimate structure of the mass. 



The accompanying figures, selected from some sixty drawings and photographs of the 

 sections obtained in the experiments, tell their own tale, and require but little description. 

 In some cases the section, although easily understood in the laboratory, is much less 

 effective when seen in photographic form. In such cases, to make the meaning clear and 



