g2 SNAKE RIVER PLAINS OF IDAHO. [bull 199. 
The linear arrangement of the scoria cones just. described, on the 
otherwise bare surface of a broad lava stream, and the nature of the 
material of which they are composed indicate that they were built 
along a fissure formed in the hardened surface of a lava stream while 
its lower portion was still plastic or liquid. They are thus of the 
nature of parasitic cones formed about steam blowholes, from which 
clots of viscous and splashes of still liquid lava, together with some 
lapilli, were blown out. The shafts of the chimney like piles formed 
about the openings in the surface of the frozen lava stream were never 
occupied by liquid lava, as their walls are far too weak to sustain such 
a pressure and no streams of lava were given off by them. 
LAVA STREAMS. 
Reference has already been made to the wide extent of the lava 
streams which flowed away from the Cinder Buttes, but it is difficult 
to convey in words an adequate impression of their magnitude, such as 
is derived from traveling over their surfaces or along their margins, 
or from a view from the neighboring mountains. 
There are six principal lava flows of recent date which have their 
origin in these buttes, and several more of considerable antiquity, the 
sources of which are now more or less indefinite. Comparatively little 
"old lava," as it may be termed, is exposed about the bases of the 
young volcanoes, except far out on the plain, and some of it may have 
come from other and distant centers of eruption. 
The place of origin of each of the six recent lava streams referred 
to is plainly distinguishable, but the best defined of all is the crater 
from which a lava stream that flowed northwestward welled out. This 
is the first fresh lava met with on leaving the road which skirts the 
west border of the Snake River Plains and taking a dim trail leading 
eastward among the Cinder Buttes. This northwest flow came from 
a crater composed of reddish tuff, the portion of which remaining has 
a height of about 200 feet. The lava rose within the tuff crater, 
breached the western side of its encircling wall, and the fragments 
floated away on its surface. The top of the congealed lava column in 
the conduit of the volcano is a semicircular plain of ropy and scoria- 
ceous basalt 500 feet across, which is continuous with the nearly level 
surface of the great sheet of lava that flowed from it and expanded on 
the plain to the northward. The place of emergence of the lava is 
surrounded on all sides, except where the breach formed by its dis- 
charge occurs, by ragged cliffs of reddish tuff. The lava not only 
broke the cone in which it rose, but it tore away the base of the outer 
slope for a distance of fully a mile before expanding on the plain to the 
northward. On each side of the hardened lava stream for about half a 
mile below its source there are precipices, similar to those partially 
inclosing the congealed pool whence it came. The right or ea-tern 
