etjssell.] RELATIONS OF THE SEVERAL ERUPTIONS. 107 
having been longer exposed to the atmosphere than any of those men- 
tioned above. The smooth swells and ridges are still bare and pre- 
serve all their corrugations, pressure ridges, etc., intact, but their 
surfaces have lost their freshness, and a little soil has been concen- 
trated in the hollows and crevices. A striking feature of this gener- 
ally bare lava surface is the presence upon it of pine trees, which seem 
to spring from the naked rock. The trees, some of which are 20 feet 
high, are gnarled and deformed, showing plainly in their contorted 
forms that their struggle for existence is severe. In many instances 
the cracks in wmich the trees have taken root are so small that they 
escape notice unless searched for. The trees are immediately sur- 
rounded on all sides by bare corrugated lava. In some examples a 
tree rises from the intersection of two cracks, where the opening is 
a little larger than elsewhere and a little more soil has been caught, 
showing how persistently the vegetation has sought for a foothold. 
The pines are scattered at intervals over an area of several square 
miles, being grouped in small groves in the hollows. They T extend to 
the bordering banks of lapilli where, finding less adverse conditions, 
they are of larger size. 
The soil gathered in the crevices and depressions of the lava is 
evidently not derived from the disintegration of the lava itself, which, 
as stated, still retains even the smaller details of its original surface, 
and is hard and black. A surface covering of lapilli and volcanic dust 
is absent, although the bordering hills are composed of such material, 
and it is evident that no explosive eruptions have caused showers of 
rock fragments to fall on the lava stream. This is a suggestive fact, 
as the volcanoes a mile or two to the west sent out their great lava 
streams after the one here considered was formed. The tuff cones 
from which they came, and the widely extended surface sheet of lapilli 
and dust on the adjacent mountains, so far as can be judged, must also 
be of much later date. The reason why the tree-covered lava stream 
escaped receiving a shower of lapilli and dust seems to be that the wind 
carried the material, which was blown out by what must be considered 
more recent volcanoes, in other directions. 
The soil in the crevices and hollows, in which the pines referred to 
have taken root, is apparently composed of ordinary atmospheric dust 
brought by the wind, a process which is still operative. 
RELATION OF THE CINDER BUTTES TO OLDER VOLCANIC ERUPTIONS. 
To the east of the tree-covered lava streams described above, still 
other local lava flows are present. Some of these can be readiiy traced 
to the craters from which they came, but they are now almost com- 
pletely soil covered and clothed with shrubs and grass, and in part 
with trees. About these and extending far be} r ond the reach of vision, 
even to an observer standing on the highest of the Cinder Buttes, are 
the vast plains underlain by still older lava sheets, but now completely 
