russell] RECENT VOLCANOES. 39 
distinct beds of compact lava in the walls of cinder cones, due to the 
running together and hardening into a single mass of many splashes 
of liquid lava, etc. 
Breached cinder cones and crags of tuff floated on lava streams. — 
There are several well-defined craters built of lapilli and scoria among 
the Cinder Buttes, which were breached by the lava that escaped from 
them, and in one instance of this nature large masses of the parent 
crater were floated away on the surface of the lava stream which 
escaped through an opening in its wall. The floated masses range in 
general from 20 to 50 feet in diameter and from 40 to 50 feet or more on 
a side. They occur in a well-defined train, extending down the lava 
stream which escaped from a breach in the parent crater for a distance 
of about 2 miles. The masses are always angular and are bounded 
by rough surfaces that have resulted from fracture. They consist of 
reddish tuff, formed by the partial consolidation of lapilli, or of adher- 
ing clots of lava that were plastic when they were brought together. 
In color and composition they correspond with the portion of the cin- 
der and lapilli cone still remaining intact, and differ from all other 
rock in their vicinity. They are in striking contrast with the black, 
generally smooth but in places wrinkled or fractured lava surface on 
which they occur. About the base of nearly every one of the crags 
the surface of the sustaining lava is depressed so as to form a moat- 
like trough which completely encircles it. Some of the features just 
described, including the depressions encircling the bases of the crags, 
may be recognized in the accompanying photographs. (PI. III.) 
It is of interest to note that the surface of several of the lava streams 
about the Cinder Buttes, for a distance of a mile or two from their 
sources, has subsided since it hardened, owing to an outflow of the 
still liquid lava from beneath a rigid crust. The amount of this 
subsidence is in several instances from 50 to 70 feet. As a result of 
such subsidence in the central part of a lava stream its marginal 
portions are sometimes left stranded, and a precipitous broken 
escarpment, facing the subsided area, borders the portion of the 
stream from which the lava outflowed. On the border of a lava 
stream which has been lowered at times large blocks of the stranded 
crust slope downward toward the subsided area. 
In the case of the Northwest lava flow, i. e., the one on which the 
crags of tuff, etc., described above, occur, there has been a subsidence 
of the surface of the flow throughout the first mile or more of its 
course, and a lowering of the crust formed on its central part of 50 to 
70 feet. A portion of the flow, a square mile or more in area on the 
west side of the stream, was left stranded by this subsidence at a 
higher level than the surface of the lava, which continued to flow to 
the north. 
From the facts briefly described above it seems evident that the 
crags of tuff, etc. , on the surface of the Northwest lava streams are 
