440 DISTRIBUTION OF PLANTS. 



the leaves of the Ilamelinia. On closer examination, the very presence 

 of plants seemed often due to the moisture of the steam-vents. I 

 was struck with the novel combination of the elements forming cli- 

 mate ; but after diligent search in the clefts, and wherever the plants 

 were exposed to superior warmth and moisture, I could detect no 

 change in species, nor even in the habit of growth. The steam-vents 

 were found to be holes descending irregularly into the somewhat con- 

 centric crevices, formed in the settling down of the country towards 

 the Great Crater, through undermining within, at the bottom. The 

 lava-surface being very porous, the steam arose from intercepted sub- 

 terraneous springs, fed entirely by the rains; for we ascertained, that 

 steam is emitted from the bottom of the crater only after falls of rain; 

 which are here rare and very slight. 



I remarked on the ground and on the vegetable growth, single 

 threads crossing each other horizontally, and entirely resembling 

 spider-webs, except in the unaccountable fashion of spinning. They 

 proved to be threads of capillary obsidian or volcanic glass ; of the 

 variety which seems peculiar to this crater, passing in cabinets under 

 the name of " Peli's hair." These seeming cobwebs are extremely 

 light, and during a slight shift of wind which I once witnessed here, 

 came floating over in tufts somewhat resembling tow. In general, the 

 threads are not seen falling, but lying singly on the surface of the 

 Leeward portion of the island ; and even high up Mauua Roa, more 

 than twenty miles from their place of origin. 



The Great Crater, like the two other lava-fountains of the Hawaiian 

 Group, is situated in the curve or angle of a distinct crevice of forma- 

 tion; as though, in first bursting forth, the molten rock had lifted a 

 scale-like portion of the Earth's crust. The crevice of formation ex- 

 tends across the whole island from sea to sea ; and to the present day 

 serves as the crevice of eruption, through which the lava takes one of 

 two directions in the emptyiLgs of the crater. The Great Crater does 

 not fill up and overflow ; but when about half full, walls of rock are 

 no longer strong enough to hold the accumulated liquid mass; the 

 island itself seems to split open to give it egress. During the discharge, 

 the central portion of the mass within the crater is drawn off; leaving 

 the remainder adhering to the sides in a wide shelf or terrace, contin- 

 uous all around, and called by residents the " black ledge." This ter- 

 race has a lake-like surface, congealed and black ; depressed below the 

 brink, according to our measurements, about "five hundred feet;" the 



