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DYNAMICAL GEOLOGY. 



lence that of Mount Loa in 1868. The extinct volcano of eastern Maui, 10,217 feet 

 high, which bears abundant marks of recent action, has a crater between 1,000 and 

 2,000 feet deep, exceeding much that of Kilauea. From two sides of it, the east and 

 north, lava-flooded valleys, one to two miles wide, go off toward the sea. They are due 

 to two fractures made at a summit-eruption, in which floods of lava were poured forth 

 and a quarter of the volcanic mountain was started from its foundations. In Oahu, 

 the eastern of its two volcanic mountains retains the regular slopes of its old volcano 

 on the sides facing southwest and south ; but on the north and northeast, a long preci- 

 pice, fluted and gorged by erosion, is a vertical section of the stratified lavas; and it 

 indicates that a part equal to two thirds of the original volcanic cone was broken off at 

 an eruption and has been lost by subsidence in the depths of the sea. 



The rock of all these eruptions is a heavy grayish-black doleryte 

 (or basalt), more or less scoriaceous ; and most of it is chrysolitic. The 

 glassy grains of this mineral make a considerable part of the sands 

 along the sea-shore reached by the eruption of 1840, and are common 

 elsewhere. The rock of fissures is often free from cellules ; and in 

 some places — as near Hilo — there are beds of solid columnar basalt. 

 Part of the basalt is porphyritic. Feldspathic rocks also have been 

 ejected in former time, and even after Mt. Loa had reached its present 

 height; but no recent eruptions of this kind have occurred. 



The feldspathic rock of the summit is free from cellules and looks like a somewhat 

 laminated phonolite. According to Dr. C. Pickering, it forms the western wall of the 

 summit crater. A similar compact feldspathic rock constitutes hills in the western part 

 of Oahu, about the central portion of a profoundly eroded volcanic mountain. 



The cooled lava of the bottom of Kilauea has a surface crust, four to six inches thick, 

 of glassy scoria, which is the hardened scum or froth; and below this it is solid rock, 

 often containing only a few ragged cellules. 



But the lava from fissures outside of the pit is usually free from the scoria ; the sur- 

 face is hard and compact, but looks ropy, owing to the marks of flowing. 



If a stream of lava stops in its course, it begins at once to harden ; then, when made 

 to move again, from another accession of lavas, the thick hardened crust breaks up, 

 like ice on a pond, but makes cakes and blocks, 100 to 10,000 cubic feet in size, black 

 and gray and bristled all over with jagged points and angles. On Hawaii, such blocks 

 lie piled together over extensive areas, making what are called there, clinker-Jit Ids ; and 

 they are regions of the most horrid, chaotic desolation. The streams of hardened lava 

 over the land often rise into great protuberances, many yards across, with oven-shaped 

 cavities within, which were formed by waters beneath that were evaporated by the heat 

 while the flow was in progress. 



2. Lipari Islands. — The Lipari Islands, north of Sicily, are all 

 volcanic, and vary in height from 1,601 to 3,125 feet. Stromboli, 

 3,090 feet high, is the northern island, and Lipari (1,601 feet) and 

 Vulcano (1,978 feet) are the southern. The points of most prominent 

 interest are the following : — 



(1.) The ejections of later times, unlike those of Hawaii, are chiefly 

 of cinders, and the volcanic mountains are largely cinder cones. 



(2.) The last lava ejection of Stromboli took place in 1786 ; since 

 then it has been in constant activity, though with varying intensity. 

 Spallanzani witnessed in 1788, and described well, its mode of action, 

 the sinking of the lava in the throat of the crater for twenty feet or 



