ORIGIN AND STRUCTURE OF VOLCANIC CONES. 49 



ing in another world of whicli 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 mo- 

 lecular constitution of matter far clearer and deeper than we are able 

 to obtain by all the refinements of laboratory analyses or the hypo- 

 thetical 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 wonder-land in which the smallest of our fellow- 

 creatures may be living, moving, and having their being. Belgravia. 



-- 



THE ORIGIN AKD STRUCTURE OF YOLCANIC 



GO^^ES. 



By H. J. JOHNSTON-LAVIS, F. G. S. 



11. 



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 ex- 

 ternal 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 tempera- 

 ture, 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 consider- 

 able dimensions, effected by one or many eruptions, we shall find that 

 certain definite changes have taken place in the chimney. The erup- 

 tion is reduced in force, there are spasmodic puff -like ejections of la- 



TOL. XIX. 4 



