russell] MANY SMALL CRATERS. 63 
absence o± centers of eruption still more secure, as they are the most 
conspicuous elevations to be seen throughout the entire extent of the 
lava plains. Although the idea that the lava reached the surface as 
immense fissure eruptions has perhaps g-ained general acceptance, my 
observations failed to sustain it, but, on the contrary, led me to con- 
clude that many local eruptions from distinct vents are accountable for 
the origin of the extensive sheets of once molten rock. While future 
studies may perhaps show that actual fissure eruptions have occurred, 
I know of no facts to sustain such a hypothesis. 
SOURCE OE THE LAVA. 
It is true there is an absence of conspicuous cinder cones on the 
Snake River Plains, and, as stated by Geikie, there is certainly no 
"central cone from which this great sea of basalt could have flowed." 
Yet a more intimate acquaintance with the region shows that there 
are several localities at which lava was outpoured from local vents of 
the ordinary volcanic type, about which scoria and cinder cones were 
formed. Besides these more conspicuous monuments of local erup- 
tions, there are many broad, low elevations built of lava of a type not 
seen by me elsewhere, and, so far as I can judge, not elearty recognized 
by other observers, which may, for convenience, be designated as lava 
craters/' Instead of an absence of local eruptions from definite vents, 
my examination showed that there are scores of such localities still 
recognizable, and suggestions of many other more or less completely 
buried beneath more recent effusions of molten rock. The well- 
defined cinder cones referred to, with more or less perfect craters in 
their summits, are represented b}^ two buttes, each between 500 and 
600 feet high, situated on the lava plain about 6 miles northeast of 
Market Lake (PI. XVI). About 20 similar elevations occur in what 
are known as the Cinder Buttes, on the west side of the Snake River 
Plains, approximately midway between Little Wood River and Big 
Lost River (PI. X), and again by Kuna Butte, 15 miles north- 
west of Mountain Home (PI. XVII). These well-defined cinder cones, 
described more in detail below, grade into another variety of eleva- 
tions, which are still more common, but may pass unnoticed until one 
becomes familiar with their characteristic forms. The elevation of this 
second variety is due to the emergence of vast quantities of highly 
liquid lava from a comparatively small and in most instances a decid- 
edly circumscribed opening, and to its outflow in all directions, except 
when it met older uplands, so as to form a low elevation with exceed- 
ingly gentle slopes and widely expanded base. These elevations are 
«The nearest approach in form and structure of any volcanic pile yet described to those referred 
to above are, so far as I can judge, the great volcanic mountains of the Hawaiian Islands. There is 
too great a discrepancy in size, as well as other features, however, between these two classes of 
examples to admit of their being referred to the same type 
