russell.] NATURE OF THE VOLCANIC MATERIAL. 75 
from a quarter of an inch up to an inch or more in diameter. This 
material was blown out in abundance and assorted more or less through 
the action of the wind, so that large surfaces are covered with frag- 
ments of a nearly uniform size. The fragments are usually black or 
various shades of red, and in certain instances have a brilliant irides- 
cence due, I presume, to changes which have occurred since they 
were exposed to the air, and which resulted in the formation of thin 
films on their surfaces. 
About the Cinder Buttes, so far as observed, there is a notable 
absence of compact, rounded kernels and stratified beds of granular 
lapilli, such as form a large portion of the Market Lake crater and 
occur in stratified sheets, associated with lacustral sediments, in the 
western part of the Snake River Plains, as for example, near Glenns 
Ferry. 
Ch>U.— The lava ejected in a highly viscous or nearly solid condi- 
tion took on various shapes, depending on its degree of plasticity, 
and perhaps also the length of its aerial flight. This lava seems to 
have been principally in the form of ragged clots, which were blown 
out by mild explosions with low initial velocities, and which fell about 
the orifices from which the}^ came, and built up scoria cones with but 
small admixtures of lapilli and dust. At times these clots adhered 
one to another or to the surface on which they fell, but more fre- 
quently they were sufficiently rigid on striking to maintain their 
shapes, and fell so gently that the rough projections were not broken. 
Evidently these masses, although solid, were not cold and brittle when 
they came to rest. They are always rough and irregular, and some- 
times have a length of a foot with a transverse diameter of only 
2 or 3 inches, but more frequently they are excessive^ irregular but 
not markedly elongate, and of all sizes up to 40 inches or more in 
circumference. 
Scoria. — Numerous masses of scoria occur also, especially in the 
walls of certain small parasitic cones. These masses present the 
appearance of having been blown out of the craters in a highly plastic 
or semifluid condition, and of having become highly scoriaceous and 
rudely spherical during their short journeys through the air. These 
rough, ball-like masses, usually 8 to 16 inches in diameter, were suffi- 
ciently soft to adhere slightly one to another on coming to rest. Their 
exteriors are rough, usually brown or reddish, but not conspicuously 
scoriaceous, while within they are coarsely vesicular and at times 
nearly hollow, as is shown in the photograph, PI. XI, .1. In one of 
these spherical masses, in the crust of which a hole had been broken, 
I found a bird's nest securely sheltered. 
Bombs. — Portions of the highly viscous and fluid lava in the throats 
of the volcanoes were in niany instances thrown high in the air, and 
