MR CADELL ON EXPERIMENTAL RESEARCHES IN MOUNTAIN RUILDING. '3o'3 



lower portions of the strata are drawn out in a highly attenuated form, and dip inwards 

 as in last experiment. At these places thrust-planes tend to originate above, and 



Fig. 22a. 



three such faults have been formed on the left side. The thrust-plane on the right, 

 formed at an earlier stage, has disappeared, as the section has now been so pared away 

 that the front is several inches farther along- the strike than at the start. The thrust in 

 question did not extend more than one or two inches inwards along the strike, and gave 

 place to the overfold now exposed. The compression has been so great that the bed 

 immediately resting on the waxcloth has been nearly nipped out altogether at the crest 

 of the central fold. Now it is clear, that when strata or rocks of any kind are thus 

 squeezed together and drawn out in a particular direction, the original character of the 

 rock will become changed. If the distortion be small, the alteration may not be at first 

 noticeable, but when, as in the figure, the thickness of any member is notably diminished, 

 and its particles forced to flow along certain planes for any considerable distance, just as 

 the puddle bar in a rolling-mill is rolled out to a great length and attenuated to a corres- 

 ponding extent, it is clear, that as the particles of the iron, when in a pasty condition, 

 are thus made to arrange themselves along the flow lines, and give the wrought bars a 

 fibrous structure, so in the rock the particles assume a new arrangement along the planes 

 of movement, and produce a foliated or schistose structure in the mass. In this minia- 

 ture mountain system, the particles in the bed next the waxcloth have all been made to 

 flow upwards to such an extent that, had the mountains been real ones, they would have 

 exhibited vertical schistosity at the core. I would here throw out the suggestion that 

 this experiment may explain how it is so common to find a core of foliated rock in 

 many of the larger alpine masses, the original crests of which have been removed by 

 denudation. I hope to repeat this experiment, and endeavour to obtain still better 

 results, as the subject is one of great importance ; and in the second part of the paper I 

 hope to discuss at greater length the physical problems on which it has a bearing. 



C. On the Relation between Folding and Regional Metamorphism. 

 These experiments are merely modifications of the interesting experiments of Prof. 



A. Favre of Geneva. 



VOL. XXXV. PART 7. 



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