klssell] MAKGINS OF LAVA SHEETS. 103 
dependent on their gradients. Where the ascent was gentle it flowed 
up them 5 or 6 miles before being cheeked by the rise of the land. 
The ridges between the mountain valleys became capes and headlands, 
and the peaks at their extremities were, in a few conspicuous instances, 
converted into islands. About 10 miles southwest of the Cinder Butte 
the lava was partially checked by a ridge of quartzite projecting well 
into the plain, but crossed it at a saddle and descended as a cascade 
about 200 feet high on its southern side. This lateral offshoot of lava 
formed a stream which, at the crest of the cliff down which it cascaded, 
was about 600 feet wide. During its maximum it was 30 to 35 feet 
higher than the surface now remaining, and left a ridge of angular 
fragments resembling a lateral moraine on each side of its course. 
Below the cascade the lava expanded and reunited with the portion of 
the main flow which went around the end of the cape and extended a 
mile or more up a lateral valley. An elevation near the end of the 
ridge across which the lava flowed was left as an island or a steptoe. 
Another saddle, now crossed by a wagon road, about 500 feet farther 
up the crest of the ridge than the lava cascade, was barely reached by 
the lava, which, however, did not flow down the southwest slope, but 
congealed after forming tongues of pahoehoe, which had started to 
descend. In a few other instances, between the Cinder Buttes and 
the southward-projecting mountain spur south of Carey, islands of 
quartzite rise through the fresh black lava. 
The wagon road between Carey and Martin follows for nearly the 
entire distance — about 40 miles in a straight line — the immediate bor- 
der of fresh lava fields, including all its sinuosities. This road, between 
the two places named, is fully twice as long as a straight line con- 
necting them. It enters nearly all of the lateral valleys as far as the 
lava extended, and winds about the ends of nearly all the mountain 
spurs that project into the plain. The highway is held rigidly to this 
course — almost a contour line— by the precipitous mountain slopes on 
one side, and by a wall of rugged lava, frequently 15 to 20 feet high, 
on the other. In this narrow, trench-like depression some fine mate- 
rial, together with fallen blocks of stone, has served to grade the 
roadway. As the Cinder Buttes are approached, the material forming 
the roadbed shows a change in character, becoming finer and consist- 
ing mainly of lapilli and volcanic dust. Between the Cinder Buttes 
and the neighboring mountain the road passes over an extensive bed 
of coarse, scoriaceous lapilli or "cinders," which from its appearance 
has been reported to be "natural coke." The dust and lapilli were 
ejected from the Cinder Buttes during their explosive eruptions, and 
showered down on the adjacent mountains within a radius of about 10 
miles, but are wanting on the more recent lava flows. The thick 
accumulation of dust in the roadway was washed down from the adja- 
cent mountain sides. 
