INTERIOR OF CRATERS. 113 



crumbles into more or less considerable shreds, and hence cones 

 are deeply broken in all manners of shape. Sometimes the whole 

 mass is swallowed at once in the abyss it covered, and is recon- 

 structed by subsequent eruptions. This took place in the terminal 

 cone of Etna, which has several times disappeared entirely, leaving 

 an immense aperture, without parapet, in the midst of a little plain 

 which crowned the original gibbosity or hill. At Vesuvius only 

 the upper part of the cone has ever been modified. 



23. Interior of craters. Contrary to the expectation of all those 

 who visit volcanoes, the interior of craters seldom possesses much 

 that is worthy of observation. After great eruptions, during which 

 they cannot be approached, these cavities (which are of conical 

 form, and have a more or less extensive diameter at the top, with a 

 bottom apparently formed of a sheet of consolidated lava, which 

 covers the principal chimney) ordinarily present for observation 

 merely jets of sulphurous vapours, escaping here and there from 

 fissures in the soil, from interstices in blocks of crumbled scoria?, or 

 a greater or less number of small cones raised up in different 

 places. Occasionally we see one or more gulfs, sometimes filled 

 with vapours which escape continually, and sometimes revealing 

 the incandescent lava in the depth; sometimes silent and dark, 

 inspiring with terror, but without possessing the least interest for 

 observation. In long intervals of crises, traces of volcanic action 

 often entirely disappear; in certain instances even the sides of 

 ihe crater become covered by vegetation, as is related of Vesuvius 

 before the eruption of 1631. 



24. There are, however, some observations worthy attention. 

 The crater of Stromboli, which has been in continuous activity from 

 the most ancient times, still presents phenomena identical with 

 those recorded by Spallanzani, in 1788. It is constantly full of 

 melted lava, which alternately rises and sinks in the cavity. Having 

 reached to twenty-five or thirty feet of the edge, this lava swells, 

 is covered with large vesicles or blisters, which speedily burst with 

 a noise, permitting the escape of an enormous quantity of gas, and 

 projecting scoriaceous matters on all sides. It immediately sinks, 

 after an explosion, then rises again, to produce the same effects, 

 which are in this way repeated at regular intervals of some mi- 

 nutes. 



25. If the lava of Stromboli were less fluid, it is conceived, that 

 havino; reached to its highest point, it would there stop, assume an 

 arched form, and become consolidated into a more or less elevated 

 cone ; and then, if an explosion occurred at a certain instant, a new 

 conical crater would be found in the middle of the old one. This 



23. What is found in the interior of craters ? 



24. What is remarked of the crater of Stromboli ? 



25. What would probably be observed, if the lava of Stromboli were ItM 

 riuid than it is ? 



10* 



