348 MB CADELL ON EXPERIMENTAL RESEARCHES IN MOUNTAIN BUILDING. 



■sole." inclined at a lower angle, along which the whole mass may have travelled for 

 considerable distances. 



It is almost unnecessary to say that the existence of such major and minor thrusts 

 has only been discovered within the last three years by the Geological Surve} 7 . But I 

 have no doubt that, when other mountain systems come to be examined in the light of 

 bhe researches by my colleagues and myself in the North-West Highlands, and in the 

 laboratory, these structures will prove to be of common occurrence.* 



B. Origin of" Thrust- Planes" and "Fan Structure.'" 



It had been my belief that the great thrusts of the west Sutherland area, the effects 

 of which have just been noted, must be connected with deep-seated folds, due to lateral 

 compression of this part of the earth's crust. Although there were no distinct traces of 

 such folds to be seen on the surface, it seemed impossible that the great thrust-planes 

 could be prolonged indefinitely downwards, at the same low inclination as they 

 exhibited wherever exposed, and the only reasonable explanation of their origin that 

 suggested itself was this, that each major thrust at a certain depth changed its angle, 

 and bending downwards gradually disappeared, the break in the strata being finally 

 represented by a single great deep-seated synclinal fold. 



To produce folding below, and study its results at the surface, the strata were arranged 

 on a flexible and inextensible band of stout waxcloth about 3 feet long and 7 inches 

 broad, the extremities of which were nailed to blocks of wood, which took the part of the 

 pressure board in former experiments. The waxcloth and end pieces were laid between 

 the high sides of the box used before. The left end piece was fixed to the sole of the 

 box, and the screw was applied to the right end piece in such a way as to throw the 

 waxcloth into a series of undulations or folds, shown in figs. 15—1 7a. 



Fig. 15. 



A layer of tenacious clay was formed on the waxcloth, above which were spread 

 strata of damp sand, stucco, and foundry loam. When pressure was applied from the 



* Compare fig- 14 with the horizontal sections in the Survey Report, loc. cit. 



