Russell.] BECENT VOLCANOES. 49 
rocky crags visible, and are covered with soil mostly of eolian origin, 
in which a strong growth of sagebrush, etc., is conspicuous. Crater 
No. 3 is less completely concealed beneath accumulations of atmos- 
pheric dust than No. 1, and is less densely overgrown with sagebrush, 
while No. 2 presents a rough surface of hard black lava, on which 
pressure ridges are conspicuous, although notable quantities of atmos- 
pheric dust have accumulated in the depressions, and bushes and 
bunch grass grow in cracks and crevices on seemingly bare cindery 
crags and ridges. 
While Craters Nos. 1, 2, and 3 are instructive on account of the 
many square miles of lava poured out from them and the various 
stages reached in its change to smooth pasture land, the chief interest 
of the general locality centers about Crater No. 4, at the north end, 
the youngest of the series. 
Crater No. Jf. — This very modern crater, unlike its companions, 
came into existence on a somewhat steep-sloping hillside, which was 
trenched by erosion channels previous to the volcanic outburst, and 
the great flood of extruded lava flowed away in one principal direc- 
tion. Owing to the freedom afforded for the escape of the lava down 
the slope below the orifice from which it came, a large portion of the 
cinder and lapilli crater, built during an early stage in the history of 
the volcano, has been spared, and furnishes important evidence as to 
the general sequence of events, which, as it now appears, normally 
accompany the building of lava cones. 
Crater No. 4, as it exists to-day, is in part a cinder and lapilli cone, 
and in part a lava cone, and extending over an area of about 50 square 
miles on its southeastern side is a black lava field entirely bare 
of vegetation (PL XII, A). Although differing conspicuously in its 
details from the associated craters in the same series, the one here con- 
sidered was evidently built in the same manner as its companions, 
but owing to its being located on a sloping surface, the products of 
the earlier stages of the eruption which built it were not buried by 
the great effusion of highly liquid lava poured out later, as was the 
case in numerous observed instances, where similar eruptions have 
occurred on a plain. 
Throughout about one-half of the periphery of the cinder and lapilli 
cone forming Crater No. 4, the older rocks, consisting mainly of Terti- 
ary rhyolite, are without a covering other than a thin layer of soil, to 
within a distance of 800 or 1,000 feet of its base. This fact suggests 
that some evidence may perhaps be obtainable as to the nature of the 
break or opening through which the eruption that built the crater 
reached the surface. The testimony in this connection, however, is 
meager. On the hillside, where the crater is situated, and extending 
in an essentially straight line from it, both to the north and south, 
there is a faint escarpment averaging perhaps 1 5 feet in height, and 
facing east. This escarpment has the general appearance of a fault 
Bull. 217—03 4 
