386 Colonel Burrard — Tlie Origin of Mountains. 



general terms, such as the following — " Every topographical feature 

 standing above sea-level is compensated by an underlying deficiency 

 of density, and that deficiency is uniform to a depth equal to ten 

 times the height of the feature " — the geodetic computer could grapple 

 with the problem. It is true that the basis of the Fisher theory 

 is that each mountain has an attenuated root, and the depth of this 

 root is always equal approximately to ten times the height of the 

 mountain above it ; but when computers come to apply this theory to 

 actual topographical features they are met everywhere with local 

 exceptions. In Northern India alone we have three such local 

 exceptions: (1) The compensation of the Himalayas is said by 

 Mr. Fisher to exist not only under the mountains themselves but to 

 extend laterally beyond the Himalayan region. How can computers 

 test a theory when the limits and size of the roots are not exactly 

 defined ? (2) According to Mr. Fisher's general proposition mountains 

 have roots and valleys have none. But the Ganges valley is an 

 exception ; here the alluvial deposits are said to have been so heavy 

 as to press downwards into the liquid substratum. It has thus a root 

 of deficient density, just as if it were a mountain. How can computers 

 deal with a valley that is not in accord with the general theory ? 

 If one valley is taken to be an exception to the general theory, how 

 many others are to be treated as exceptions? (3) An advocate of 

 the Fisher theory, writing in Nature, May 8, 1913, discusses the 

 Himalayas and their isostatic compensation. He then dismisses the 

 Vindhya Mountains and their compensation as though they presented 

 a different problem to be treated differently. But geodetic computei's 

 cannot alter their formulae to suit every geological peculiarity ; they 

 must be given a general theory which is applicable to the Himalayas, 

 Vindhyas, Alps, and other ranges. They cannot compute Himalayan 

 effects alone, and subsequently examine Yindhyan effects alone, 

 for the two are interdependent. Computers have to regard Asia as 

 a whole, and deal with it as such. 



5. Two theories of mountain compensation have been placed 

 before geodesists — Mr. Hayford's and Mr, Fisher's. According 

 to the former the depth of compensation is everywhere the 

 same, namely 70 miles, but the degree of compensation is larger 

 for high mountains than for low. According to Mr. Fisher's 

 theory the degree of compensation is always the same, but the 

 depth to which that compensation extends is greater for high 

 mountains than for low. Mr. Hayford varies the amount of 

 compensation by altering its degree ; Mr. Fisher varies it by altering 

 its depth. 



Now if we test these two theories as stated above by the geodetic 

 results of America and India we find Hayford's strongly supported 

 and Fisher's contradicted. Hayford's theory assumes constancy of 

 depth, and this assumption we find borne out. Fisher's assumes 

 a greater depth of compensation for high mountains than for low, and 

 this we do not find borne out. Hayford's theory is applicable to 

 a solid globe ; Fisher's is not. Hayford's has explained both the 

 large negative values of g that have been always found by observation 

 to exist in the interiors of continents, and also the large positive 



