VOLCANOES. 733 



so ; its rising again ; then the swelling up of great bubbles over its 

 surface, made by the vapors in their effort to escape ; finally, the 

 bursting of the bubbles, and the ejection of the material to a great 

 height, to fall as cooled cinders ; and so on, in constant succession at 

 short intervals. 



(3.) The ejections of the northern island (Stromboli) are of the heavy 

 doleritic or basaltic kind ; those of the southern (Lipari and Vulcano), 

 are trachytes, or the lighter feldspathic ; while in the intermediate 

 Panaria group (a half submerged volcano) they are of intermediate 

 character, called trachydolerytes by Abich. But on Stromboli there 

 are older feldspathic kinds at the centre. The trachyte of Lipari is 

 mostly quartz-trachyte (called Liparite), a rock having nearly the con- 

 stitution of granite ; and with it occurs volcanic glass, or obsidian, 

 which is sometimes in streams that bear evidence of sluggish, twisting 

 flow. Pumice, a common variety of the scoria, is an article of export 

 from the islaud. (See further on the Lipari Islands, J. W. Judd, 

 Geol. Mag., 1875.) 



3. Vesuvius. — Vesuvius is nearly 4,000 feet in height. It is the 

 remains of a large ancient crater, part of the walls of which consti- 

 tute the ridge on the north, called Somma. 



(1.) It is remarkable for large and lofty cinder ejections, and fre- 

 quent outflo wings of lava. The mountain, with the region at its base, 

 consists of lavas, beds of tufa, and cinders, interstratified with one 

 another, but with the tufa most abundant below, and the cinders of- 

 ten forming a high cinder cone at the top of the mountain. The cin- 

 der ejections of 1779, according to Sir Wm. Hamilton, were thrown 

 to a height of 10,000 feet. The fact proves (1) the vast projectile 

 force of the bursting bubbles in the crater ; and (2) the great viscidity 

 of the lavas. 



(2.) In preparing for an eruption the great crater has become, by a 

 more or less gradual process, filled by the lavas ; and this has sometimes 

 gone on until the depression at the top, or the crater, had disappeared, 

 and a broad lava plain surmounted by a cinder cone formed the sum- 

 mit. At the same time, the ejections of fiery cinders have increased in 

 frequency from one in five or ten minutes, to an uninterrupted volley 

 of them ; and then, the sides of the mountain, on one side or another, 

 have been broken, and the lavas have flowed out, emptying the crater 

 once more and revealing a gulf perhaps one or two thousand feet deep. 

 Thus, with all the irregularities, the action is in a general way similar 

 to that of Hawaii. 



(3.) The eruptions have usually been attended by heavy earth- 

 quakes, unlike those of Hawaii. 



(4.) In its eruptions, the sea has sometimes had access to the fires 



