russell.] RECENT VOLCANOES. 45 
surface and, additional material of the same character being supplied, 
form tile-like sheets. This entire sequence is admirably illustrated 
by the projectiles which accumulated to form the Cinder Buttes. 
The occasional presence of balls of dense lava on the surfaces of lava 
flows, described by J. D. Dana in the case of certain lava streams in 
the Hawaiian Islands, and observed by me in Idaho, a as well as the 
presence of analagous spherical masses of lava in the crater walls of 
certain of the Cinder Buttes, suggest, as a tentative hypothesis, that 
during the boiling of lava in a crater, masses of fused rock may become 
cooled, and, owing to rotation produced by the movement of the molten 
or plastic material about them, acquire a spherical form before being 
blown out or carried away by outflowing lava. The compact, rough- 
surfaced, spherical balls sometimes found about volcanoes appear to 
have originated in some such manner, and not from the rotation of 
plastic material projected into the air. 
The sequence of events in the history of the Cinder Buttes, as 
recorded by the accumulations of projectiles still remaining and by 
the extensive lava flows which were discharged from the same volcanic 
vents, is briefly as follows: The eruptions in a large number of 
instances began, so far as can be judged from the evidence now avail- 
able, with explosions which caused considerable quantities of cool 
and rigid lava in the form of lapilli, dust, etc., to be projected into the 
air. Later came similar violent discharges of plastic lava which formed 
scoria and volcanic bombs, and later still, liquid lava was ejected. 
This fell before cooling, and spreading over the surface where it 
struck formed lava cakes. Following these explosive discbarges, 
or accompanying the later ones, great volumes of highly liquid lava 
were poured out. This lava was extruded quietly and flowed over the 
surface of the surrounding plain so as to form sheets many square 
miles in area. The close of the eruptions, in several instances at 
least, was not characterized by a return of the conditions which pro- 
duce explosions, but the outflow of liquid lava decreased gradually 
and finally ceased, the craters being left with nearly level floors of 
highly vesicular rock having the surface characteristic of pahoehoe. 
Lapilli cones, cinder cones, etc. — The term cinder cone is commonly 
used to designate the piles of projectiles which have accumulated 
about volcanic vents, irrespective of their precise character. While 
the cones and craters referred to are in general composed of irregu- 
lar scoriaceous masses of lava, usually referred to as "cinders," it 
will be seen from the brief description given above of the wide range 
in the nature of the projectiles of which they are composed that sev- 
eral varieties of "cinder cones" should be recognized. 
When angular fragments of hard lava, such as blocks of rock, lapilli, 
dust, etc., are blown out of volcanic vents, they usually fall about 
the opening from which they come and accumulate in a conical pile 
a Bull. U. S. Geol. Survey No. 199, p. 114. 
