J. D. Dana — History of the Changes in Kilauea. 33 



and annexed -to the succeeding lava-flow. But the evidence 

 against great tufa deposits, excepting those from lateral ejec- 

 tions, is, I believe, sufficient ; and by great I mean 50 or 100 

 feet ; not the 1000 feet and more common in the regions of the 

 Rocky Mountains and the Pacific border. 



On the island of Maui, I found no such beds of projectile 

 origin in the walls of Haleakala, or in those of Wailnku valley 

 the probable crater cavity of western Maui. On Oahu, the 

 pitch of the layers of lava along the Manoa and Nuuanu val- 

 leys is only 1° to 3°; and in the precipices and bluffs which 

 bound them I saw no layer of tufa. The thick tufa deposits 

 are confined to cinder and tufa cones, and these are common.* 



This point needs investigation ; for the existence of even 

 thin tufa beds in alternation with the lava beds of the great 

 volcanoes of the islands, may still be true, and such facts would 

 have much interest. 



5. The crater of a has alt-volcano is the same in origin, history 

 and functions as those of volcanoes of other kinds, hut differs 

 usually inform. — The crater of a great volcano probably has 

 always its beginning — -as I set forth in my Exploring Expedi- 

 tion report— in a great discharging fissure. But once open, it 

 usually continues open until a temporary or final decline of 

 volcanic action, whatever the kind of volcano. It continues 

 open because (1) of the fixed position of the supply conduit; 

 because secondly of the conduit-work going on through it in 

 the discharge of vapors and lavas ; and because, thirdly, of the 

 down-plunges in the crater consequent on the undermining 

 which the discharge of the conduit occasions. The open end 

 of a deep-reaching conduct determines thus, by its discharges 

 and the subsequent underminings, the existence of the crater ; 

 and the crater, by the work done within and about it, makes 

 the volcanic cone. This appears to be the order of rank or im- 

 portance in the phenomena — the crater begins in the opened 

 fissure and is the indicator and future builder of the cone. In 

 the history of the volcano, the era of summit outflows may 

 pass, and only lateral discharges take place ; and still the dis- 

 charge of vapors from the lava conduit and the accompanying 

 movements in the lavas, together with the down-plunges in the 

 crater following the discharges, will keep the crater, or por- 

 tions of it, in continued existence, and the work of eruption or 

 outflow, if subaerial, is still adding to and shaping the cone. 



This is the present stage of Kilauea and Mt. Loa ; and these 

 are the results as they exemplify them. The action, functions 



* The cinder or tufa deposits of lateral cones have often great extent. This is 

 well seen on Oahu where Diamond Hill, Puuchbowl, and the region about 

 Aliapaakai or the Salt Lake, are examples. 



Am. Jour. Sci.— -Third Series, Vol. XXXV, No. 205.— Jan., 1888. 

 3 



