THE STRENGTH OF THE EARTH'S CRUST 313 



in India where the deflections of the plumb-line are actually in 

 opposition to the directions called for by isostasy/ The major 

 elements of the relief, the Himalayas, the plateau of India, and the 

 surrounding ocean basins are of course largely compensated, but 

 these figures show that in detail the hypothesis of complete isostasy 

 is very far from the truth. Crosthwait suggests that the explana- 

 tion for the difference between the United States and India probably 

 lies in the magnitude of the recent upheavals of the crust in that 

 part of the globe. Nevertheless such upheavals cannot exceed the 

 strength of the crust, and in India, therefore, perhaps may be better 

 observed than in the United States the maximum strains which the 

 earth is competent to endure. 



It may be concluded, therefore, that the convergence of geodetic 

 evidence shows the crust to be competent to sustain loads measured 

 by the weight of several thousand feet of rock extending over 

 circular areas some tens of thousands of square miles in area. 

 This is a measure of crustal strength twenty, fifty, or even a hundred 

 fold greater than that advanced in recent years by the leading cham- 

 pions of high isostasy. 



FURTHER GEODETIC WORK NEEDED EOR GEOLOGIC PROBLEMS 



It has been the intention in the preceding analysis to show two 

 things: first, that the data set forth by Hayford and Bowie are of 

 great value to geology and establish new methods of research, 

 but, second, that the difficulties inherent in the observations and 

 their mathematical treatment, and the fewness of the stations in 

 comparison with the heterogeneity of the earth, are such that the 

 conclusions from the geologic study of deltas in the first part of 

 this paper are as convincing and perhaps as accurate as the present 

 results of the geodetic studies. The latter, however, opens for 

 the whole earth a field of investigation which the geologic evidence 

 covers very locally and imperfectly, a world-wide field which should 

 be pursued for the geologic as much as for the geodetic bearings. 



By means of the divining rods of pendulum and plumb-line the 

 heterogeneities of mass and the loci of strain in the outer crust of 



' "On the Origin of the Himalaya Mountains," Professional Paper No. 12, Survey 

 of India, 191 2, 



