ON THE VOLCANIC PHENOMENA OF JAPAN. 



42 & 



kine's ' Civil Engineering,' we may say that the average strength of Fnji- 

 ean lies betw^een that of rnbble work and sandstone. Iwaki-san, Nantai- 

 san, and Alaid are like good rubble masonry, while the strength of the 

 ill-fated Krakatoa is not much above that of ordinary brickwork. In 

 making the above calculations I have used : 



1. The profiles of volcanoes traced from photographs which I used in 

 my original communication on the forms of volcanoes published in the 

 ' Geological Magazine.' 



2. A series of tracings from photographs of Fujisan and other moun- 

 tains not hitherto published. For most of these a scale can be obtained. 

 The best scale for Fujisan is probably the difference in height of Hoyei- 

 san and the summit. Hoyei-san is a parasitic crater on the southern 

 side of Fuji and in the profiles is marked H. This difference in height 

 is about 4,137 feet. 



A scale may also be obtained from the line of sea-level or from the 

 diameter of the crater, which is about 750 metres. 



Two profiles of Fujisan from the surveys of Mr. 0. Schiitt are also given. 



Causes modifying the natural curvature of a mountain and therefore 

 interfering with the above calculations are : 



1. The tendency, during the building up of the mountain, of the 

 larger particles to roll farther down the mountain than the smaller 

 particles. 



2. The effects of atmospheric denudation which carries materials 

 ■from the top of the mountain down towards the base. 



3. The position of the crater and the direction in which materials are 

 ejected. 



4. The existence of parasitic craters on the flanks of a mountain. 



5. The direction of the wind during an eruption. 



6. The sinking of a mountain in consequence of evisceration beneath 

 its base. 



7. The expansions and contractions at the base of a mountain due to 

 the acquisition or loss of heat before and after eruptions. 



9. Theoretical Moimtains, 

 As it might be interesting to compare actual mountains with theo- 

 retical mountains constructed from the equation i/=|j[-- - j such 



mountains have been drawn. 



The values of c are given in the following table : 



In drawing up the table, I have taken the instantaneous breakino- 

 strength of granite and its crumbling strength, which is the largest 



