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THE POPULAR SCIENCE MONTHLY, 



last spoken of acting together. In Fig. 2 are seen two varieties, one 

 assuming a spire-like form. These may make their appearance any- 

 where on the volcano, but are usually situated in close proximity to 

 the vent. Their size varies from twelve inches in height upward ; 

 generally from three to thirty feet. They are commenced in the major 

 number of cases in the jBssured crust recently formed over still-flowing 

 lava. Here the .vapor escapes in spasmodic puffs, and by its force a 

 small quantity of lava is forced up and spread out around the aper- 

 ture, which rapidly cools. It is followed by another puff and another 

 oozing of lava above and around the aperture of the first. In this 

 manner layer by layer is built up, thus giving an irregular, imbricated, 

 roll-like appearance to the exterior. The surface is rapidly covered by 

 brilliantly-colored sublimates, and the fumarole then presents a very 

 pretty spectacle. The author lately was able to thoroughly watch the 

 formation of such a fumarole some twenty feet high, its decadence 

 and disintegration extending over a period of eight months. On pass- 

 ing the arm down the central tube. (i. e., the fumarole was extinct), it 

 could be felt very regular and smooth, and having a pretty uniform 

 bore of about nine inches. 



After one slight eruption, the fumarole in question presented a 

 very curious phenomenon. Immediately (about two or three seconds) 

 after the explosion from the main vent, there came three terrific bangs, 

 with a spout of vapor from its apex, the last one shooting out small 

 fragments of still liquid lava. 



This continued without variation for six hours that the author re- 

 mained in the crater. The spire-like form may be varied according to 



Fig. 3. Crater of Deposition. 



surrounding circumstances. If the escape take place along a fissure, it 

 will assume on occasions a miter-like form. There are many other 

 varieties in form, depending on the variability of surrounding circum- 

 stances. 



It is now necessary to draw attention to the great difference of 

 opinion which has been expressed upon a point for which we have 

 very little data to support either of two views of the question. 



Vuleanologists were for a long time divided into two schools, 

 which often waged war against each other with considerable fierceness. 

 The so-called upheavalists were led by such eminent men as Von 

 Buch, Elie de Beaumont, and Humboldt ; whereas those who held the 



