72 SNAKE RIVER PLAINS OF IDAHO. [bull. 199. 
between normal cones built of cinders, lapilli, etc., with well-defined 
craters, and other examples of a similar nature partially destroyed by 
lava Hows which came later, and including, as the other extreme of the 
series, low, broad mounds, without craters, apparently formed entirely 
of lava flows. For this reason, and also because a sufficient number of 
the volcanoes have not as yet been studied, the classification suggested 
above will not be attempted. The study of the volcanoes of the Snake 
River Plains is best begun by a visit to the most recent and freshest 
of the series. None meet these requirements better than a group of 
volcanic cones termed the Cinder Buttes. 
CINDER BUTTES. 
LOCATION. 
Close to the west border of the Snake River Plains, in their widest 
part, midway between Cary and Martin, and nearly 70 miles due west 
of Blackfoot, there is a group of cinder cones surrounded by vast lava 
flows. These now extinct volcanoes are of recent date, are remarka- 
bly fresh in appearance, and furnish most instructive illustrations of 
the nature of the eruptions which deluged such a large part of south- 
ern Idaho with lava. The most conspicuous of the cinder and lapilli 
cones in the group of elevations here referred to is indicated on the 
General Land Office map of Idaho as "Old crater." To the residents 
of the region this conspicuous cone is known as Cinder Butte, and I 
have thought best to term the entire group of volcanoes, of which it 
is a part, Cinder Buttes. 
The most conspicuous of the Cinder Buttes (see PL X) rises with 
steep slopes to a height of 600 feet above the surrounding plains and 
is distant about 5 miles from the base of the bold mountains, composed 
of granite and quartzite, to the west, which sharply define the west 
border of the northeastern extension of the Snake River Plains. The 
volcanic mounds and cones comprising this group form a well-defined 
belt 3 or 1 miles wide, which begins abruptly at the base of the adja- 
cent mountains and extend out on the vast plains in a southeasterly 
direction for from 10 to 15 miles. The buttes are most closely placed, 
and in fact much crowded at the western end of the belt, and become 
wider apart and even isolated in its eastern part. Detached from the 
main group, and about 5 miles southward from the highest of the 
buttes, are two small elevations, probably lapilli cones. 
TUFF CONES AND CRATERS. 
The elevations comprising the Cinder Buttes are composed, to a 
large extent, of angular fragments, such as dust and lapilli, blown out 
during violent eruptions. Lapilli, being a technical term, is used to 
