338 Pi'of. J. Milne — On the Form of Volcanos. 



of their contour, and secondly the fact that these contours appear to 

 be similar. Pre-eminent amongst the regularly formed volcanos of 

 Japan with which I am acquainted I may mention Fusiyama, 12,365 

 feet, near Yokohama; Ganjosan, 7000 feet, near Morioka; Chokaisan, 

 6000 feet, between Niigata and Akita ; Twakisan, 5000 feet, near 

 Awomori ; and Kumagatake, 2700 feet, near Hakodate. 



If we look at the profile of these mountains near their summits, 

 we might be inclined to call them conical; but if we look at them 

 as a whole, as we descend we see this upper cone expanding and 

 sweeping outwards, forming a graceful curve. The causes which 

 might produce or subsequently affect this form may be summed 

 up as follows, 



1, The position of the crater. If this is central and remains in that 

 position during successive eruptions, we may expect the mountain 

 to be regular in form. 



2, If the eruptions of a mountain are irregular in their action 

 and character, the above regularity may be destroyed. Thus by 

 paroxysmal outbursts portions of a cone might be removed, — if 

 lava is erupted at one time and not at another, or if it accumulates 

 on one side of the mountain more than on another, these are all causes 

 which would seriously interfere with any regularity of contour, 



3, Any outbursts on the side of a mountain, or formation of 

 parasitic craters, will also tend in the same direction, 



4, Even if the crater should be central, but the direction in which 

 the lapilli and other materials were projected shoiild be towards one 

 side more than another, as I sometimes observed was the case at the 

 eruption of Oshima in 1877, the regularity of the piling up will 

 also be interfered with, 



5, The direction of the wind during an eruption will also in- 

 fluence the shape of a mountain. On the Yedo side of Fusiyama 

 the slope is less than upon the opposite side. This I believe is in 

 part due to the wind, which at the time of the last eruption of that 

 mountain, in 1707, was blowing in the direction of Yedo. 



6, The nature, that is, the size, the specific gravity, the porosity, 

 etc, of the materials thrown out will during the actual accumulation 

 and subsequent consolidation give a character to the curve of the 

 slope. 



7, Lastly, we have the effects of denudation continually drawing 

 material to lower levels and sculpturing and modifying the original 

 contours. As this action will generally take place more or less 

 uniformly on all sides of a mountain, it will be a cause tending not 

 so much to destroy the regularity of a volcano as to alter the 

 character of its slope. 



When considering the various causes which may produce denu- 

 dation, we must remember that there generally will have been more 

 action near the summit of a mountain than near the base. Thus, for 

 example, more water falls at the top of a mountain than below, and 

 therefore the little streamlets which cause disintegration will be 

 more active at the top of a mountain than at the bottom — the activity 

 diminishing gradually towards the base. One of the tendencies of 



