Page:Popular Science Monthly Volume 19.djvu/59

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THE ORIGIN AND STRUCTURE OF VOLCANIC CONES.

ing in another world of which we have no knowledge and can form no definite conception. We, by our senses of touch and vision, know the shapes and colors of objects, and by our very rudimentary olfactory organs form crude ideas of their chemistry or composition, through the medium of their material emanations; but the huge exaggeration of this power in the insect should supply him with instinctive perceptive powers of chemical analysis, a direct acquaintance with the inner molecular constitution of matter far clearer and deeper than we are able to obtain by all the refinements of laboratory analyses or the hypothetical formulating of molecular mathematicians. Add this to the other world of sensations producible by the vibratory movements of matter lying between those perceptible by our organs of hearing and vision, then strain your imagination to its cracking-point, and you will still fail to picture the wonderland in which the smallest of our fellow-creatures may be living, moving, and having their being.—Belgravia.

 
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THE ORIGIN AND STRUCTURE OF VOLCANIC CONES.
By H. J. JOHNSTON-LAVIS, F. G. S.
II.

IT is observable in certain volcanoes that the lava frequently strewed around after an eruption contains more or less perfect spheres, consisting of a hard external coat and more scoriaceous contents, and these from their resemblance are known as volcanic bombs. Their contents may be divided into two classes:

1. Scoriaceous vesicular lava, identical in composition with the external shell.

2. Miscellaneous, such as altered masses of lapilli, loose blocks of foreign materials caught up in the current of lava. These balls are generally considered to be formed by the masses being ejected to great heights, and cooling as they whirl through the atmosphere.

This seems improbable, as on falling they would inevitably smash into a thousand fragments. It would appear more likely that they are simply concretionary in structure around a nucleus of low temperature, solidifying on the surface a layer forming a crust of lava. Let us now direct our attention to the minor particulars, such as the changes of the crater, and metamorphism, or alteration of the already ejected materials. If the volcano has already reached some considerable dimensions, effected by one or many eruptions, we shall find that certain definite changes have taken place in the chimney. The eruption is reduced in force, there are spasmodic puff-like ejections of la-