Extinct Volcanoes in Colorado. — Lakes. 41 
there was no bridge, I waded the stream and ascended the 
(opposite bank. The bank proved to be a rugged cake of lava 
from fifty to one hundred feet thick. The central portion was 
of hard, massive, dark grey basalt showing a fluidal structure 
and a few small steam holes. Above this were masses of 
scoria piled up or tumbled along in chaotic confusion like the 
clinkers of a slag furnace. Underneath also, the lava was 
scoriaceous. It resembled pictures of the recent lava fields of 
Mauna Loa, or Vesuvius. The blocks of scoria were highly 
vesicular like honey-combs. The edges of the little circular 
steam holes were as fresh and sharp as if the flow had occurred 
but a week ago, and were not filled by zeolites and amygda- 
loids as is the case generally we believe with basaltic flows of 
an older date. The surface of a greater part of the flow is 
destitute of vegetation, a black rugged mass of slag and clink- 
ers. Towards the opposite side of the valley, decomposition 
of the lava allowed a sparse covering of grass and sage-brush. 
I had no difficulty in tracing the flow across the valley to 
the entrance of a narrow ravine in the hills. Great rugged 
masses of scoria were adhering to the sides of the ravine, as if 
a furnace had poured molten iron down it. Erosion had re- 
moved the lower portion of the lava, and bitten into the sand- 
stone forming the bottom of the ravine. Following up the 
ravine for about a mile into the hills, the lava stream became 
more continuous, and appeared eventually to issue in a huge 
semicircular, bulging mass, from the top of a hill of very steep, 
smooth outlines. This hill, with all the surrounding hilltops 
at this level, for a circular area of about a mile in diameter, is 
composed of, or covered with grey "lapilli," little pebbles of 
scoria mixed with fragments of shale and red sandstone, from 
the size of a pea to that of a hen's egg, shot up by the explo- 
sive steam from the throat of the volcanic vent. These beds 
of "lapilli" appear to be of considerable thickness. At the top 
of the hill they seem to have been consolidated into a coarse 
stratified breccia, tipped up at an angle of 5 or 10 degrees on 
either side of the great mass of lava, as if the lava had broken 
through this portion of the crater and tilted up the brccciated 
sandstone in its exit. 
Climbing over the lava mass, I stood on the top of the hill, 
and look down into a perfect oval-shaped crater, the bottom of 
which lay upward of GOO feet below me. The walls of the era- 
