340 Trof. J. Milne — On the Form of Volcanos. 



by a heap of loose dirt, an engineering friend has shown me that 

 it follows from Kankine's theory, notwithstanding that the same is 

 incomplete, that the surface is that which would be produced by a 

 simple logarithmic curve revolving about an axis, — consequently 

 such a heap would have a slope diminishing from the top to the 

 bottom. Looking over my note-books, amongst the steepest slopes 

 which I have observed upon the sides of volcanos in Japan, I may 

 mention the following: Fusiyama, 30°; Asamayama, 28°; Ganjosan, 

 31° ; Twakisan, 30° ; and Kumagatake, 40°. The first four of these 

 are outside slopes taken near the top of the mountain. The last 

 observation was made upon a slope of angular blocks of stone 

 inside an old crater. 



Mr. Scrope gives the slopes of volcanos as being from 20° to 35°, 

 towards the base diminishing to 10°, and gradually ultimately to 

 horizontality. However, whilst fully recognizing the nature of the 

 true slope of a volcano, the sketches which illustrate works treating 

 of this subject are, so far as can be judged by rough measurements, 

 somewhat misleading. For example, to quote from the pictures in 

 the works of no less a person than the great Humboldt, " Umrisse 

 von Vulkanen aus den Cordilleren von Quito und Mexico," I find 

 that, by rough measurement, the slopes of several volcanos must be 

 as follows :— Cayambe Uren, 18,170ft., about 53°; Elcorazon, 

 14,820ft., 53° to 69°; Chimborazo, 17,712ft., 55°; and Ilinissa, 

 16,362ft., 55°. Whether these Matterhorn-like inclinations really 

 represent reality or not, I do not know, but I should be inclined to 

 think that artistic feeling may have caused them to have been 

 unintentionally augmented. 



Form of Volcanos. — The general form of a volcano has already 

 been suggested whilst speaking of the inclination. To quote more 

 fully from Mr. Scrope, he says, " It should be remarked, however, 

 that the dykes being more numerous near the central vent, their 

 aggregate effect in elevating these beds will be greatest there, and 

 give tliem a steeper elevation near the summit than lower down the 

 flanks of the mountain. This is one cause (but by no means the 

 principal one) of the angle of the slope of the higher beds, and of 

 the outer slope likewise, usually ranging from 20° to 35°; while 

 towards the base it diminishes to 1 0°, and graduates ultimately to 

 horizontality. The more influential causes of this general result 

 are (as will shortly be shown), the frequency of lateral eruptions on 

 the lower slopes of every volcanic mountain, loading them with 

 parasitic cones and floods of lava, and the abundance of fragmentary 

 matter carried down the heights by rain and floods — all combining 

 to enlarge the base." ^ Whilst fully agreeing with the form which 

 is here described, the causes which are indicated as having been the 

 principal ones in the production of such a mountain form, although 

 no doubt, influential, are, I should think, by no means the principal 

 ones. Of the greater number of volcanos which I have seen in 

 Japan, the only method which I have had of obtaining their general 

 form and curvatures has been by sketching. Of two of them, 

 1 Scrope, Volcanos, p. 167. 



