Trof. J. Milne — On fhe Form of Volcanos. 343 



The right side is left out, because it is so very irregular. 



No. V. is not calculated, because it is probable that the only 

 photograph which I have may have been taken from a picture. It 

 is, however, useful as showing, as compared with the others which 

 are drawn, a similarity in curvature. 



Considering that these investigations have been open to so many 

 errors, the picture being a perspective view, it being small and 

 difficult to make measurements upon, there being no accurate method 

 for obtaining a true axis, there being many small irregularities in the 

 mountain itself, — the fact that the calculations made from different 

 pictures should all so closely approximate to each other is evidence, 

 I think, sufficiently converging for us to accept the result towards 

 which it points. 



That this result should agree with that obtained for the stability of 

 a self-supporting mass of loose materials is very striking, and seems 

 to show, notwithstanding its roughness and the observations to 

 which it has been applied, an invariable concurrence. 



This being the case, I think we are justified in regarding mountains, 

 similar to those about which I am now writing, as having a form 

 mainly due to the simple piling up of material, and not as cones 

 which have been subsequently modified by a number of secondary 

 causes, such as are advocated in treatises on Physical Geology and 

 Volcanos. 



Probable Existence of an Internal Core. — Observing that the slight 

 discrepancies which do exist in the values of ^ are due to variations 

 in the curvature near the top, and at the base of the mountain it was 

 suggested that these might not only be due to external modifying 

 and sculpturing actions, like those pointed out by Mr. Scrope, but 

 also, perhaps, to the action of an internal core. If we pour sand 

 upon a table, it ought to form a heap, with sides like those of a 

 Japanese volcano; but if we first place a small box on the table, and 

 pour sand on the top of it until it is buried, the shape of the heap 

 will be considerably altered. If, instead of a box and sand, we take 

 a mountain like Fusiyama, and imagine it to have a core which is 

 tolerably flat, such as ^wje might have expected from the more modest 

 of the advocates of an elevation theory, the result would be that the 

 present base of the mountain would be considerably contracted, 

 because in this case the core is capable of resisting a greater pressure 

 than an equal bulk of cinders could resist. Above the core the 

 curve would be logarithmic, from which we may conclude that if 

 any core exists in the mountains about which I have been writing, it 

 is probably below the lowest line at which measurements have been 

 made. To enter fully into the effect which a core would produce 

 upon the external form of a mountain, is a calculation into which 

 friction would enter as an important factor. 



If, from the shape of any given mountain, it were supposed that 

 it had been built up round a more or less cylindrical core, it would 

 be interesting to calculate the diameter of this core for various 

 heights. This also can be shown to be logarithmic in form. 



Building up of a Volcanic Mountain. — The eruption at the island 



