Status of the Theory of Isostasy. ■ 333 



of 330 kilometers, and under the plains in front, to a 

 depth of 60 kilometers. The sums of the residuals were 

 reduced to the smallest amount if the depth of com- 

 pensation was taken at 600 kilometers in Western India, 

 330 kilometers in Eastern India, and at the surface in 

 Southern India. 33 The solutions, however, show inde- 

 terminate results in several of these cases, in that there 

 are two minima to the sum of the residuals for increas- 

 ing depths of compensation. Hayden notes that the 

 number of stations is too few to give reliable averages, 

 but considers it as probable that the conditions beneath 

 the Himalaya are in reality different from those beneath 

 the other provinces of India. The results also point out 

 what is evident from the United States, that other varia- 

 tions from the condition of perfect isostasy are of more 

 influence upon the residuals than assumed variations in 

 the depth and distribution of compensation. Hayden 

 reached a conclusion similar to that of Crosthwait : that 

 the problem of isostasy in India is much more compli- 

 cated than in the United States. Hayden finally con- 

 siders the evidence from the intensity of gravity, and 

 concludes from the deficiencies over the plains that the 

 trough filled by the Indo-Gangetic alluvium is a broad 

 basin sloping gently inwards toward the Himalaya, from 

 which it is separated by a steep wall resulting from the 

 series of reversed faults which separate the older geo- 

 logical systems from the younger. 



The interpretation has thus far brought forth a prob- 

 able great depth of compensation beneath the Himalaya, 

 permitting an isostatic support of the great mountain 

 masses without requiring very great differences in crustal 

 density; an alluvial trough depressed in front of the 

 mountains and filled with alluvium of lesser specific 

 gravity than the normal crust ; and a belt of excessive 

 density to the south of the geosynclinal trough. This 

 belt exerts a strong gravitative influence equivalent to a 

 mountain ridge and has become known as the Hidden 

 Range. 



To those who note only the discrepancies between the 

 facts of observation and the Hayford hypothesis, the 

 whole theory of isostasy may appear shaken. Hobbs 

 goes so far as to state: "Applied in the region where 



33 H. H. Hayden, Notes on the relationship of the Himalaya to the Indo- 

 Gangetic plain and the Indian peninsula, Becords Geol. Survey India, 43, 

 pt. 2, 138-167, 1913. 



