How Mountains Are Formed' 



By R. A. Lyttleton 



Reader in Theoretical Astronomy 

 University of Cambridge 



[Witli 2 plates] 



The existence of mountains has remained for generations one of 

 the most perplexing- problems of geology and geophysics despite the 

 enormous amount of evidence apparently available. True, we lia\'e 

 been told since childhood that mountains are due to shrinkage of the 

 Earth as it cools causing corrugations as on a withered apple. But 

 a purely verbal explanation of this kind represents only the first 

 glimmerings of a theory. Before any theory can be regarded as satis- 

 factory, it has to show that all the proposed processes would occur 

 to correct numerical amount. If experiments are not possible, this 

 can be done only by working out the mathematical consequences of 

 ]3hysical laws. A verbal theory can keep the moon swinging around 

 the Earth with a piece of cotton, but as soon as numbers are put into 

 the scheme it founders. This has happened to various theories of the 

 origin of mountains. 



The geologist can explore the surface of the Earth in all its detail. 

 As yet, the prospector can bore down only a small distance, but he 

 can examine present surface rocks and features that must formerly 

 have been buried much deeper. The geologist can see sedimentary 

 layers, which were originally deposited horizontally, so compressed 

 from the sides as to be folded and contorted here, and sheared and 

 thrusted layer-over-layer there (pi. 1, upper fig.), and also uplifted 

 and turned through large angles. He can examine lands that at one 

 time formed seabeds, and he can examine intrusive rocks and lavas 

 poured out in seemingly gigantic amounts from volcanoes. He can 

 tunnel through mountains and examine them in all their forms. This 

 has been done on an immense scale but has produced few clues as to 

 the ultimate cause of mountains except to show that worldwide com- 

 pressive forces have been at work. The origin of the forces has 

 remained a mystery. 



^ Reprinted by permission from Discovery (London), vol. 25, No. 2, February 1964. 

 766-746 — 65 25 351 



