74 SNAKE RIVER PLAINS OF IDAHO. [bull. 199. 
Like several of the associated cones, it has no crater at the summit, 
but terminates in a rounded weather curve, the symmetry of which is 
somewhat broken by crags of dark-red tuff. 
The remnants of crater walls in several instances frequently exhibit 
well-defined stratification, the layers in the outer portion t)f the once 
conical pile dipping away from its center in all directions at low 
angles. An increase in dip occurs from the first-formed or lowest 
layers to the higher ones, owing to the greater thickness of material 
deposited immediately about the orifice than at a distance from it. In 
the best section of a ruptured tuff and cinder cone observed the lower 
beds are nearly horizontal, while those about 80 feet above dip 
outward at an angle of 20°. The inward-dipping beds forming the 
funnel within the rim of a crater dip much more steeply than the outer 
layers, but are usually not well preserved. In the section of a crater 
just referred to the position of the former opening is shown by a con- 
fused mass of tuff and cinders which, in part, seems to have reached 
its present position by falling from above. 
CHARACTERISTICS OF THE EJECTED FRAGMENTS. 
The fragments of volcanic rock which occur in such abundance at the 
Cinder Buttes, and of which the walls of the craters themselves are 
built, may be classified as dust, lapilli, scoria?, clots, bombs, and lava 
cakes. To classify it in still more general terms, this material may 
be divided into two classes: First, lava which cooled and hardened in 
the crater from which it was ejected and was broken into fragments by 
steam or gaseous explosions, the fragments being sufficiently rigid 
not to undergo a change of shape during their aerial flight except, 
perhaps, by fracture on coming in contact with other fragments in 
the air or on striking the ground; and, second, lava which was pro- 
jected into the air in a plastic and even liquid condition and assumed 
various shapes either during its passage through the air or on falling. 
There is no sharp division between these two classes, however, and a 
series of specimens grading from angular fragments to rounded bombs 
and thin, flat lava cakes formed by the spreading and cooling of 
splashes of highly liquid lava on striking the earth, might easily be 
collected. 
Dust dtid lapilli. — The material which presumably hardened on the 
surface of liquid lava within a crater and was broken and blown out 
by steam or other explosions and fell about the opening from which 
it came or was widely distributed by the wind, consists mainly of 
angular fragments of highly scoriaceous lava which vary in size from 
dust particles to irregular masses several inches, and in some instances 
1 or 2 feet in diameter. The most common product of this process is 
highly vesicular lapilli, composed of rough, angular fragments ranging 
