ORIGIN OF FOLDED MOUNTAINS — PROUTY 305 



The present-day theories taken as a whole account for all the 

 observed facts in connection with mountain building, but it will be 

 many years before there can be a general agreement as to the most 

 important cause of either mountain folding or mountain uplift. 

 Fortunately some of these theories can be tested. Exact longitudi- 

 nal determinations, by use of radio, over a period of years, should 

 give definite information concerning the drift of continents. Inten- 

 sive geophysical tests should continue to yield facts about the earth's 

 interior. Tidal and processional forces are being checked by the 

 mathematicians. Geologic materials and structures are being scru- 

 tinized, with the new theories in mind. In short the subject is under- 

 going a rigid quantitative analysis. 



We shall probabh' find that in the great work of mountain build- 

 ing, not one or two causes, but many causes, are active, and that 

 not all folded ranges are built in the same way. 



LITERATURE 



D.\LT, R. A. 



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Jolt, J. 



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