VOLCANIC PHENOMENA. SOLFATARAS. 115 



daytime like a heap of smouldering ruins. The descent, to the ledge appears 

 to the sight a short and easy task, but it takes an hour to accomplish. 



"All the usual ideas of volcanic craters are dissipated upon seeing this. 

 There is no elevated cone, no igneous matter or rocks ejected beyond the 

 rim. The banks appear as if built of massive blocks, which are in places 

 clothed with ferns, nourished by the issuing vapours. 



** What is wonderful in the day, becomes ten times more so at night. 

 The immense pool of cherry-red liquid lava, in a state of violent ebullition, 

 illuminates the whole expanse, and flows in all directions like water, while 

 an illuminated cloud hangs over it like a vast canopy." 



27. Solfata'ras. There are a great many craters which for a 

 long time have not given exit to any lava, and are reduced to dis- 

 engaging, in greater or less abundance, sulphurous gas, which 

 escapes by a multitude of fissures in the soil, and often accompa- 

 nied by aqueous vapour. Hence the name of Solfata'ra has been 

 given to those places where these phenomena are more or less 

 developed. There are some craters which seem to have been 

 always in this state. Such, for example, is the Solfata'ra of Pouz- 

 zouli, in the kingdom of Naples, which is a vast crater of eleva- 

 tion, at the bottom of which are found broken volcanic rocks, daily 

 decomposed by the vapours. This solfata'ra is of the highest anti- 

 quity, and appears never to have presented other phenomena than 

 those now observed. When in repose, volcanic craters become 

 more or less active solfata'ras. 



28. It is not uncommon to find one or more lakes, frequently of 

 great depth, at the bottom of craters and solfata'ras. The waters 

 they contain are sometimes quite pure, but they are often charged 

 with various salts, or sulphurous or sulphuric acid, as was seen 

 in the volcan of Teschem, in the island of Java, prior to 1817, 

 the year when this mountain was entirely destroyed by the action 

 of gas. 



29. Commencement of eruptions. Continuous emissions of e^s 

 or scoriaceous matter from certain volcans, must not be confounded 

 with eruptions, which are sudden events, fortunately transitory, 

 often bringing desolation over an entire country. When an erup- 

 tion is about to take place it is ordinarily preceded by earthquakes, 

 after which it suddenly occurs with more or less noise. If a volcan 

 already exist in the country, an eruption begins by pouring out 

 abundant fumes, composed of various gases and aqueous vapour, 

 then pulverulent matter called volcanic ashes, the quantity of which 

 is sometimes immense ; then foilow directly, when they do not 

 appear from the beginning, fragments of red-hot porous stones, 

 called rapiUi or lapilli and pouzzolani, more or less considerable 

 blocks of solid matter, which are sometimes ejected to great dis 



27. What are Solfata'ras ? 



28. What is the character of the water of lakes found in craters ? 



29. How is the commencement of eruptions characterized .' What are 

 volcanic ashes? What is rapilli^? What are volcanic bombs? Wh%f IP 

 tu'fa ? 



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