SUMMARY. 229 



minor changes in the distribution of land and water have occurred not 

 only frequently, but we can scarcely believe otherwise than that the 

 forces which have resulted in the intricate folding and crumpling of 

 the great sequence of sedimentary and crystalline strata must have 

 been of very long duration, and were probably existent from the very 

 earliest date when the first grain of sediment was deposited in the 

 Himalayan seas. We can go further. Whatever other — and as yet 

 only dimly understood — forces were at work to produce this contrac- 

 tion and folding of the earth's crust, we know of two forces about 

 which there can scarcely be the slightest doubt. The first is the 

 gradual cooling of our earth, and consequent lessening and shrinking 

 of the surface of it. Secondly — and this is a force which may be 

 mathematically expressed — we know that the centrifugal force endea- 

 vours to move every point on the surface of the earth in a direction 

 opposite to that in which gravitation attracts it. 



The actual force exerted is the resultant between the centrifugal 

 and tangential forces, and it has the tendency, if I may so express it, 

 of gradually moving each point on the surface of the earth towards 

 the equator. It may be supposed that an enormous sequence, of 

 to a certain extent pliable deposits, trying to move bodily, as it were, 

 towards the equator, but en route arrested and banked up against a 

 rigid mass of which the peninsula of India is a small remnant only, 

 must necessarily have suffered wrinkling, and lateral crushing. 



These forces operated since the earth existed and must be active 

 now. But throughout the great sequence of the palaeozoic, mesozoic 

 and kainozoic deposits we search in vain for an internal explanation 

 of the great unconformities and disturbances of coast-line which have 

 taken place at certain intervals, such as I have sketched out above. 

 That these changes were not local overlaps only is apparent when we 

 compare the Central Himalayan area with the Perso-Afgha*n region. 

 In the latter the physical changes are far more clearly marked. At 

 the close of the carboniferous epoch, which was one of pelagic condi- 

 tions in the Hindu Kush area, Khorassln and Persia, the distribution 

 of land and water must have considerably changed, as we find imme- 



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