J. D. Dana — Eruptions of Kilauea and Mt. Loa. 103 



crust of solid lava outside, or consist of a series of concentric 

 layers. 



Dr. H. J. Johnston Lavis, who has studied with much care 

 the Yesuvian lavas and eruptions, shows in his paper on u Frag- 

 mentary Ejectamenta of Volcanoes,"* that the " volcanic 

 bombs" of writers on European volcanoes are not bombs any 

 more than those of Mt. Loa ; that they were not projected into 

 the air ; that they occur scattered over lava streams in great 

 numbers when the adjoining country is free from them, and 

 occur within lava streams ; that they vary in size from a wal- 

 nut to some cubic yards, and yet have often a thin shell and 

 friable nucleus ; that they " occur most commonly by far on 

 the surface of lava-streams whose surface is rough and scoria- 

 ceous, instead of corded." He regards them as formed of 

 lapilli that fell upon the flowing lava, and " in consequence of 

 its forward motion became incorporated with it, and may un- 

 dergo partial fusion, but usually congeal around themselves a 

 coating of the parts in which they are involved." The descrip- 

 tion shows that the bomb-like masses of Hawaii are essentially 

 identical in origin with the " volcanic bombs " of Europe. 

 Ejected Mocks are, as Dr. Johnston- Lavis remarks, wholly 

 different in origin. 



4. Lateral Cones. 



Lateral cones are a frequent result of eruptions on Hawaii 

 and the other islands of the group, although the lavas are 

 basaltic. They occur, as in other volcanic regions, along the 

 courses of fissures ; along a flow of lava where fissures for sup- 

 plying lavas are underneath it ; and also in and about the sum- 

 mit crater. Whether they consist of lava-streams, or of cinders 

 (lapilli) depends on the supply of heat as well as of lava in the 

 vent (xxxv, 28) ; and whether the cinders make cinder-cones or 

 tufa cones, on the supply of moisture connected with the erup- 

 tion, much descending moisture giving a mud-like flow to the 

 ejected cinders, whence the low angle and saucer-like crater of 

 the tufa-cone. 



They appear to be most common over the lower portion of 

 a lava-stream, toward or along the sea-border ; and it may be 

 that this is due to the presence of more subterranean waters 

 about the lower or foot slopes. A lateral cone of either of the 

 three kinds is good evidence of a fissure beneath as a source of 

 the ejected and pericentrically deposited material ; and this 

 evidence from them gives their occurrence especial interest. 

 Where a stream of lava enters the sea and makes a cone of 

 cinders or lava, there must be a fissure to supply the lavas and 



* Proc. Geologist's Assoc, London, ix, No. 6. 



