Geology and Mineralogy. 397 



flowing eastward far toward Torcigno. M. Abich, who was then, 

 as he reports, studying the volcano, after describing the top-plain 

 and its cinder-cone as seen by him before the event, states that at 

 the eruption, that platform of lava subsided and opened to view 

 the interior of the large cone.* 



Another great eruption took place in January of 1S39, sending 

 forth large streams of lava, and leaving a great funnel-shaped 

 crater at top, 300 feet deep. The mode of origin of the depres- 

 sion is not stated; but it may well have come chiefly from the 

 discharge of lava, for three years of quiet intervened before the 

 emptied mountain had again much activity in the crater.f The 

 " altopiano " was again the top of the filled crater before the close 

 of 1845, but no prominent eruption occurred before 1850, and this 

 left the summit-plain at the top occupied mostly by two very 

 broad and low cones each with a deep crater. 



The processes at Vesuvius are essentially those of Kilauea, and 

 the variations in amount of subsidence about the active lava vents 

 are similar. But in the crater of more liquid lavas, Kilauea, the 

 discharge occasioning the subsidence or collapse is almost wholly 

 that of outflowing lavas, the upward discharge by the projectile 

 force from rising vapors being small. 



The lava eruptions are spoken of above as through fissures, 

 because the descriptions show this to be as much the fact at 

 Vesuvius as at Kilauea. The forces engaged break the sides of 

 the mountain along the upper or the lower slopes, or both, on one 

 side or the other of the cone, and the lavas flow out, leaving dikes 

 as registers of the number and directions of the ejections. The 

 overflows from the summit are insignificant compared with outflows 

 from lower levels ; the cup is full it is true ; but nearly all the 

 lava is below the level of the top. Von iiuch's observation that 

 the lava of 1805, shot suddenly, before their eyes, from top to 

 bottom of the cone in a single instant, or, as a calculator inter- 

 prets it, " many hundred feet in a few seconds," repeated by 

 Lyell and others, is explicable only on the view that a fissure 

 or a series of fissures opened down the mountain and let out 

 the lavas " in a single instant " from top to bottom. Fissures 

 can be opened, as Kilauea shows, without an earthquake to 

 announce the event. j. d. d. 



3. Eruption at Kilauea, Hawaii, in March, 1886. — Honolulu 

 papers of the loth of March J report the sinking and disappear- 

 ance of the lavas of Kilauea, implying, thereby, their discharge by 

 some outlet. On the evening of Saturday, March 6th, the Old 

 and New Lakes of liquid lavas in the great pit-crater, Kilauea, 

 were unusually full and brilliantly active, as seen from the Vol- 

 cano House, on the northeast edge of the great pit ; and an ac- 



* Erlaut. Abbild. Vesuvius und Aetna, Berlin, 1837. 



f Scacchi (loc. cit.) gives a sketch of the crater when in the quiet state, and 

 another showing its condition in October, 1843, after the filling of it had again 

 begun. 



% The editors are indebted for the papers to Mr. Alexander, Surveyor General 

 of the islands. 



