322 H. F. REID ISOSTACY AND EARTH MOVEMENTS 



eludes that they have passed through many periods of intense folding, 

 and that they may be a continuation of the Preeambrian Purana rocks of 

 the Peninsula. 10 



For the same reasons the Siwaliks must have been compressed before 

 they were elevated, and their folds must continue in the lower beds of 

 the Ganges basin. 11 



The many steep faults, with a reverse attitude, show that the Hima- 

 layas were under horizontal pressure when the movements on the faults 

 took place: indeed, the folding of the late Tertiary strata of the Siwaliks 

 shows existence of horizontal pressure after they were deposited ; but the 

 small hade of the faults also shows that vertical forces were dominant in 

 causing the uplift. 12 



Harden tells us that the Lesser Himalayas are a dissected peneplain: 

 and a peneplain could not be raised by compression without entirely ob- 

 literating its character. It must have been lifted by vertical forces. 



These considerations lead us to the conclusion that the Himalayas were 

 not raised to their present altitude by the compressional forces which 

 folded their strata, but that the folding occurred at an earlier period, 

 and the elevation came later, as the effect of vertical forces. We can 

 picture the following order of events: Strong compression at several 

 periods, with folding and faulting of the older rocks when at a lower 

 level: elevation of the chain by successive steps, with displacements along 

 the steep faults : great fhiviatile erosion, depositing the lower beds of the 

 Ganges plain, of which the present Siwaliks formed a part: further fold- 

 ing, involving these lower beds, but probably not the strong Himalayan 

 rocks: vertical movements, raising both the central mass and the Siwaliks 

 to their present positions; continued erosion in the mountains and depo- 

 sition in the plains. 



The great steep faults between the Alps and the Po Valley and on the 

 west side of the Wasatch Mountains show that these ranges also owe their 

 elevation, at least in part, to vertical forces. 



This brief review embraces the most important mountain ranges in the 

 world, and shows beyond question that they were raised up and not 

 squeezed up. and that the time of their elevation was distinctly later than 

 the time of folding. The same conclusion could be extended to many 



10 H. II. Hayden : Notes on the relationships of the Himalaya to the Indo-Gangetie 

 Plain and the Indian Teninsula. Records of the Geol. Survey of India. 1913. vol. 43. 



11 This hasin bears a striking resemblance to the Appalachian trough, as worked out 

 by Hall. We wonder if it represents the early stages of a great mountain chain which 

 will be a successor of the Himalayas. 



12 R. D. Oldham has reached the same conclusion. Manual of the Geology of India, 

 second edition, p. 474. 



