276 W. BOWIE THEORY OF I80STASY 



General of India. In professional paper number IT of the Trigonomet- 

 rical Survey of India, entitled "Investigations of isostasy in Himalayan 

 and neighboring regions," Burrard reviewed the literature dealing with 

 the negative anomalies at gravity stations located on the Cenozoic forma- 

 tion in India, especially the Indo-Gangetic plain, and outlined briefly the 

 attempts which had been made to explain the persistent negative sign. 

 In this book he quotes from special publication number 40 of the United 

 States Coast and Geodetic Survey, as follows: 



"In India there is a broad belt of recent geologic material running approxi- 

 mately east and west at the foot of the Himalaya Mountains. The stations 

 on the recent formation, which no doubt is largely due to the deposition of 

 materials eroded from the mountains, have in general negative anomalies. It 

 is impossible that the addition of materials could make the pressure less than 

 normal on the surface at the depth of compensation. We may therefore con- 

 clude that isostatic adjustment probably follows the deposition of materials, 

 and that the negative anomaly is probably due to the lighter materials in the 

 upper crust." 



Following this quotation from special publication number 40, Colonel 

 Burrard said : 



"In consequence of Bowie's contention that the negative anomalies are evi- 

 dence of the isostatic compensation of the Gangetic trough, I have lately made 

 a series of calculations to test the correctness of this view. Although in the 

 past I had never been able to perceive any strong geodetic evidence either for 

 or against the isostatic compensation of the trough, I am now of the opinion 

 that Bowie's contention is probably correct; for reasons which I will subse- 

 quently explain, I consider that the evidence available favors the view that 

 the C4angetic deposits are compensated." 



Burrard also stated in his book that he agreed with the speaker that it 

 may be possible to ascribe the negative gravity anomalies to the Cenozoic 

 formation. 



Isostatic Adjustment of Delta Formations 



Delta formations have been held by some geologists to be evidence of 

 the ability of the earth's crust to withstand heavy loads. 4 But such evi- 

 dence as we have at hand indicates that values of gravity on delta-forma- 

 tion areas are as nearly normal as the values of gravity stations on the 

 Cenozoic material, which is inland from the coast, such, for instance, as 

 the Indo-Gangetic plains. Wherever we have gravity stations on deltas, 



* Joseph Barrell : The strength of the earth's crust. Journal of Geology, vol. xxii, no. 

 1-8. 1914 : vol. xxiii. nos. 1, 5, and 6, 1915. 



Bailey Willis : Discoidal structure of the lithosphere. Bull. Geol. Soc. Am., vol. 31. 

 no. 2, June, 1920. 



