Ltrra Foims. 23 



bridged for the mule by lava slabs and fragments, a shaky struAure, and I was alwaA'S 

 glad when they were not too wide for my agile animal to leap. Fortunately we had 

 no fogs, and no symptoms of mountain sickness. I felt, however, that if a storm had 

 overtaken us, we should have had little chance of holding to our trail ; a light fall of 

 snow would have concealed it." More important ascents we will record later. 



General Character of the Lavas ol Hawaii. 



N 



I DO not intend to enter fully into the many analj-ses of the products of the 

 Hawaiian volcanoes, but simply sketch the coarser composition and the external appear- 

 ance of the lavas, that mv reader who is not familiar with these volcanoes may better 

 understand the descriptions that follow of the activities of the volcanoes and the ejected 

 material met with in crater or lava-stream. 



Of the two general classes into which geologists have divided lavas, the acid or 

 trachytic, — Trachyte, Obsidian, Pumice, Granite, — and the basic of which Basalt or 

 Dolerite is the type, we have on Hawaii only the latter class. Basalt contains a feld- 

 spar having more lime than soda, augite, sometimes in well defined crystals, chrysolite 

 or olivine in green nodules, often agglomerated, but generally diffused through the 

 mass, and almost invisible to the naked eye. Magnetite is also present, and rarely 

 Mica. Silica, Iron, Soda, and Lime are the final constituents. 



When the ordinary lava is thrown into the air as in the tremendous fountains 

 that often accompany the eruptions of Mauna Loa, drops are thrown off, and, caught 

 on the currents of hot air, spin out a glass}' filament sometimes exceeding three feet in 

 length. These glassy threads are local!}' called "Pele's hair" (Fig. 15), and in the crater 

 of Kilauea, as also wherever jets of lava are thrown up, they are constantly forming 

 during the ordinary active condition. When the lava cools rapidly, as in these threads, 

 the strudlure is glassy: when the coo'.ing is slow the texture is stony: this is well 

 shown in the impression of an actual specimen of rope-lava shown in Fig. 19. The 

 outside is compact, while as we pass to the interior the cells grow larger and the 

 magma is stone-like. The less fusible portion of the lava often separates in a rough 

 form (Fig. 16); the more fusible, like Pele's hair, retains its ducftility in a surprising 

 manner until the high temperature of the air in which it is formed is considered. 

 Lengths of three or four feet have been found spun from the fountains of lava on the 

 slopes of Mauna Loa during an eruption. The plasticity of the molten lava is well 



"A fuller account of this ascent was publishc-il in the American Journal of Science in iSHS, and this will be 

 inserted later with the accounts of the eruption of that year ( 1880-81 ). 



[401] 



