280 BECKER 



and the hyperbolic sine curve for this value of c are given in 

 the first illustration, PL XIII, Figs, i and 2. The easiest 

 method of making a comparison is to trace the mathematical 

 locus on a bit of thin paper and lay it over the picture of the 

 mountain. The value of c thus found corresponds to 2,627 feet. 



In 1885, I computed the value of c from 4 surveyed cross- 

 sections of Mt. Shasta, finding for that case a value of 2,640 

 feet, while for the neighboring smaller mountain. Sugar Loaf, 

 I got 2,560 feet. It is certainly a very remarkable circumstance 

 that a photograph of Mayon gives a value of c only 13 feet 

 lower than that found for Shasta, or to within a half per cent, 

 the same value. The rocks of Shasta are chiefly andesite, 

 largely olivinitic, associated with some basalt, and therefore 

 extremely similar to those of Mayon. It would appear also 

 that, in spite of the great variation which the manner of cooling 

 and other accidents attending eruption must induce in the con- 

 tinuit}^ and grosser physical qualities of the lava, the mean 

 strength of the rock at these two localities, distant from one 

 another so many thousand miles, is almost exactly the same. 



While the similarity in strength and in lithological composi- 

 tion of Shasta and Mayon is \Q.xy noteworth}', it does not follow 

 that all andesitic volcanoes would show similar vahies of the 

 constant c. The rock of Shasta is chiefly of the rough porous 

 type called by Giimbel trachytic andesite and by me asperite. 

 On the other hand, Fujisan appears to consist of pyroxene 

 andesites of the denser basaltic type. Professor Milne applied 

 my theory to this famous mountain and found as the mean of 

 several determinations from photographs and surveys c = 4,490 

 feet.' I reached substantially the same value by constructing a 

 cross-section of Fuji from the topographical map issued by the 

 Geological Survey of Japan in 1887. The section was taken 

 along a line bearing N. 36 ^X^ E. and gave c = 4,462 feet. 

 This section and the theoretical curve are shown in Text-fig. i 

 and agree most satisfactorily. 



I have from time to time met with a great number of photo- 

 graphs of volcanic cones, especially in Central and South 

 America, which agree admirably in form with the hyperbolic 



'Trans. Seismological Soc, Japan. Vol. 9, Pt. II.. p. iSo, 1SS6. 



