G32 



VESUVIAN MINERALS 



[Ch. XXV. 



ejections of lava and scoriae, in 1828, it was always sur- 

 rounded by a flat pool of semi-fluid lava, into which, scoria 

 and sand were thrown. 



In the steep semicircular escarpment of Somma., which 

 faces the modern Vesuvius, we see a great number of sheets of 

 lava inclined at an angle of about 26° and in some rare cases 

 of 30° and more. They alternate with scorise, and are inter- 

 sected by numerous dikes from two to four feet thick, which, 

 like the sheets of lava, are composed chiefly of augite, with 

 crystals of leucite, but the rock in the dikes is more compact, 

 having cooled and consolidated under greater pressure. I 

 saw one dike two feet thick composed of leucite and augite 

 in that part of the wall of the Atrio called Canale del In- 

 ferno, which was as vesicular as ordinary lava ; but this case 

 is quite exceptional. Some of the dikes cut through and 

 shift others, so that they have evidently been formed during 

 successive eruptions. 



Vesuvian minerals. — A great variety of minerals are found 

 in the lavas of Vesuvius and Somma ; augite, leucite (called 

 by the French amphigene), felspar, mica, and olivine are 

 most abundant. It is an extraordinary fact, that, in an area 

 of three square miles round Vesuvius, a greater number of 

 simple minerals have been found than in any spot of the same 



dimensions on the surface of the globe, 

 only 380 snecies of simnle minerals 



Hairy 



>le minerals as known to him; and 

 no less than eighty- two had been found on Vesuvius and in 

 the tuffs on the flanks of Somma before the end of the year 



Some 



1828. Many of these are peculiar to that locality, 

 mineralogists have conjectured that the greater part of these 

 were not of Vesuvian origin, but thrown up in fragments 



some 



& 



plosions burst. But none of the older rocks in Italy, or 



assembla 



seems 



inclination to admit that, in times so recent in the earth's 



Natm 



in the creation of new and rare compounds. Had V€ 

 been a volcano of high antiquity, formed when nature 



Wanton'd as in her prime, and play'd at will 

 Her virgin fancies, 







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