Geology. 285 



2. Investigations of Isostasy in Himalayan and Neighbouring 

 Regians; by Colonel Sir S. G. Bxjrrard, 88 pp., 2 plates, appen- 

 dixes 1 and 2, and map of India. Professional Paper No. 17, 

 Survey of India, Dehra Dun, India, 1918.— This is a welcome 

 report from India on the subject of isostasy. For many years 

 there has been some doubt in the minds of geodesists and geolo- 

 gists in India as to whether isostasy is as nearly perfect in India 

 as it has been found to be in the United States. The present 

 report seems to eliminate all doubt on this matter. The author 

 states that ''In the last few monhs, while making experimental 

 calculations I was led to the conclusion that the evidence which 

 we have regarded as unfavourable to the theory of isostasy may 

 be found to prove an unexpected support for it. ' ' 



The author reviews the opinions of various investigators in the 

 subject of isostasy in India and the results of their work. He 

 pays particular attention to the geodetic observations in the form 

 of values of the intensity of the force of gravity at stations on 

 the Gangetic plain and near it and deflections of the vertical at 

 stations in various parts of India. The gravity values over the 

 Gangetic plain have shown anomalies (difference between the 

 observed and the computed values of gravity) which in nearly all 

 cases are too light. This fact was the principal reason for the 

 conclusion that the Gangetic plain was under compensated, that 

 is that the material in the column under this area has less mass 

 than normal. 



Colonel Burrard, in this publication, accepts the opinion of 

 William Bowie, of the U. S. Coast and Geodetic Survey, in regard 

 to the possiblities of an area of recent geologic formation having 

 negative gravity anomalies being in an isostatic condition. He 

 quotes the following from Special Publication No. 40 of the 

 U. S. Coast and Geodetic Survey, entitled "Investigations of 

 Gravity and Isostasy ' ' : 



"In India there is a broad belt for recent geologic material 

 running approximately 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 impos- 

 sible that the addition of materials could make the pressure less 

 than normal on the surface at the depth of compensation. "We 

 may therefore conclude that isostatic adjustment probably fol- 

 lows the deposition of materials and that the negative anomaly is 

 probably due to the lighter materials in the upper crust." 



Following this quotation from Bowie's publication, Burrard 

 writes : 



"In consequence of Bowie's contention that the negative anom- 

 alies are evidence of the isostatic compensation of the Gangetic 

 trough, I have lately made a series of calculations to test the cor- 

 rectness 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 



