THE CRUST OF THE EARTH. 



and often scattered over the surrounding country to vast distances. 

 Sometimes the matter thus thrown up is in a state of pasty fusion, 

 and is incandescent, scoriaceous, and pumiceous. In this semi-- 

 fluid state it is projected sometimes to a distance, and sometimes 

 it flows in streams along the slopes of declivities, or collects in a 

 sheet or layer of more or^ less thickness round the crater from 

 which it is ejected. 



127. These volcanic phenomena have been already, in part, 

 explained in our Tract on Earthquakes and Volcanoes, but their 

 connection with the condition and history of the crust of the 

 earth is so close, and the aids they afford for the explanation of 

 geological phenomena so important, that it will be necessary here 

 further to enlarge upon them. 



In the month of May, 1808, the ground in the island of San 

 Jorge, one of the Azores, in the midst of an open plain and culti- 

 vated fields, was suddenly upheaved, after which it cracked at 

 several places with a terrific noise. A vast cavity or crater was 

 formed in the middle of it, having an area of nearly thirty acres, 

 and surrounded within the distance of three miles by from twelVe 

 to fifteen smaller craters. An enormous quantity of scoriaceous 

 and pumiceous matter was projected from it which covered the 

 surrounding ground to the depth of five feet for an extent of 

 twelve miles in length by three in breadth. Streams of molten 

 matter issued from it, which continued to flow for more than three 

 weeks from the principal crater to the sea. 



128. The Monte Nuovo, which was formed upon the Neapolitan 

 coast in the Bay of Baise in 1538, presents an example of like 

 phenomena. A violent earthquake had prevailed for two years, 

 which, on the 27th and 28th of September, 1538, suddenly 

 increased so as to be attended with incessant movement of the" 

 ground day and night. The plain extending between the Lake of 

 Averno (the ancient Avernus), the Monte Barbaro and the sea 

 was then suddenly upheaved, and various crevices were formed* 

 in it ; the ground, rising still more, assumed the form of a moun- 

 tain. During the succeeding night, the summit of this mountain 

 opened with prodigious noise, and vomited great masses of flame, 

 accompanied by pumice stones and ashes. The eruption con- 

 tinued for seven days, the matter ejected filling up the Lucrine 

 Lake. Since this eruption the most perfect tranquillity has 

 continued at this place. 



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