344 SEE— THE CAUSE OF EARTHQUAKES. [October 19, 



trachytic mountain was suspected by Bouguer and La Condamaine, 

 though, as Humboldt remarks, the evidence was unsatisfactory 

 (Cosmos, Vol. V, p. 30). Yet the foregoing theory enables us to 

 recognize that the similar widely extended indications of modern 

 geodesy can hardly fail to be real; and according to the principle 

 of continuity the law thus found for certain mountains must be held 

 to be general for all the great peaks and chains of our globe. In 

 fact the satisfactory explanation of this long-standing geodetic prob- 

 lem would seem to be one of the strongest arguments which could 

 be adduced in favor of the truth of the present theory of mountain 

 constitution and formation. For the facts of geodesy are based upon 

 exact observation and experiment, and unbiased by any theory ; and 

 yet they become intelligible only when interpreted by means of a 

 general theory like the present. The support thus furnished by a 

 wide body of geodetical facts would seem to place the theory of 

 mountain constitution on a basis where it may become a useful 

 adjunct to the principles of geodetic measurement. 



Probably no measurements involving long distances upon the 

 earth have so high an order of accuracy as those of geodesy. Is it 

 too much to hope that the principle of mountain constitution here 

 outlined may become the means of still greater refinement, in the 

 triangulation of the earth's surface ? 



In his well-known work on the " Figure of the Earth," ^ Pratt 



announces a proposition: 



" To deduce from the previous calculations some probable conclusions re- 

 garding the constitution of the earth's crust. The first thing to be observed 

 in the results given in the last paragraph is the very small amount of the 

 resulting deflection at the two extremities of the Indian Arc — Punnse close to 

 Cape Comorin, and Kaliana the nearest station to the Himalayan Mountains; 

 whereas the effect of the Ocean and Mountains has been shown to be very 

 large. This shows that the effect of variations of density in the crust must 

 be very great, in order to bring about this near compensation. In fact the 

 density of the crust beneath the mountains must be less than that below the 

 plains, and still less than that below the ocean-bed." 



Again :^ 



" The circumstance already noticed, that at seven coast stations out of 

 thirteen the deflection is toward the sea, seems to bear testimony to the truth 

 of the theory, that the crust below the ocean must have undergone greater 



^ " Figure of the Earth," 3d edition, p. 134. 

 '^ Ibid., p. 136. 



