98 J. D. Dana — Emqitions of Kilauea and Mt. Loa, 



of solidificlecl lava more or less scoriaceous is usually formed 

 about the vent by the pericentric action. These cones are 

 mentioned in the descriptions of all the outbreaks, not except- 

 ing that of 1880, which was visited by Rev. E. P. Baker. 

 Large deposits of cinders, or a light scoria, are sometimes dis- 

 tributed over the adjoining region, and Pele's hair is also a com- 

 mon product ; the former where the lava is thrown up in 

 fountains and partially cools exteriorly as it falls (p. 28), and the 

 latter from the action of either the fountains or the low jets 

 (xxxv, 221). 



The summit crater of Mt, Loa, unlike Kilauea, is often left, 

 after an eruption, with one or more cinder-cones on the bottom ; 

 the larger of them usually in the southern portion of the crater. 

 They are probably made from the lavas as the heat declines 

 with the first commencing movements of an eruption. 



2. Bate of flow.— The great flow of 1852, so grand in its 

 fountains and twenty miles long, was finished in twenty days ; 

 this gives, for its mean rate of progress, a mile a day. The flow 

 of 1859, thirty -three miles long, occupied only eight days, which 

 corresponds to a rate of four miles a day on a mean slope of 1 

 foot in 15. The thirty miles to Hilo in the stream of 1880-81 

 took nine months ; and the mean slope was 1 foot in 13 or 

 about 5 degrees. 



The general conditions in the flow of a great stream, its ob- 

 structions and modes of overcoming them, are well described 

 by Mr. Coan (p. 20). As to actual rate of flow, we want more 

 precise facts. It is difficult to reconcile the facts stated on 

 these points ; and especially the various velocities attributed to 

 the different portions of a flowing stream, for example": the re- 

 ported rate in one of the tunnels of "10 miles an hour " with 

 a rate for the front of the flow of " one mile a week." The 

 difficulty is still great if we suppose the 10 to be only 10, and 

 whatever the obstructions along the front. The conditions are 

 those of a discharging faucet, and the flow below is that of the 

 liquid after its escape spreading widely over a rough surface. 



The many openings through the crust of a stream into the 

 tunnels which give out vapors, and often have the shape of 

 jagged cones, suggest the possibility that a fissure may exist 

 beneath in these and similar places for the discharge of lava 

 and vapors. But the idea that such fissures generally underlie 

 a lava stream (which I formerly thought probable) is opposed 

 by Mr. Coan ; and there are not facts to sustain it except for 

 the Mt. Loa stream of 1868 and the Kilauea for 1810. 



The tunnels of a stream, made by a crusting of the surface 

 while the lava continues flowing beneath, have a smooth, some- 

 what glassy or enamelled interior, with horizontal flutings and 

 mouldings which were made by the moving lava. In a tunnel 



