4 Geology, &c. of the country west of the Rocky Mountains. 
a brook flowing into the Lewis river, which we pursued through a 
deep break in the mountains, observed some days before in the west. 
These were found to consist of sparry limestone, and sandstone. Con- 
tinuing our journey still in a N. W. direction through a broken coun- 
try, across a larger branch of the Lewis river, and over a mountain of 
rock similar to the.one last mentioned, we came toa plain, open only 
to the north and surrounded by snowy mountains. The rounded 
stones and gravel observed here, were all compact gray sandstone. 
At this place, where we remained some days, we observed that thun- 
der showers come uniformly from the S. W. and not from the W. 
and N. W. as on the Atlantic. 
The last of July we left this place, travelled S. and recrossed the 
mountain and Lewis river, the country to a great extent bemg much 
broken. We met with limestone of different kinds, and with sand- 
stone. 
We saw, also, for the first time, nigh the river, at probably one 
hundred miles from its source, resting on pudding stone, a stratum 
of dark porous rock, evidently of volcanic origin. 
Leaving the river and going S. W. over a mountain of sandstone 
and sparry limestone, arranged in strata, highly inclined to the hori- 
zon, we encamped on a creek with high bluffs, composed entirely of 
volcanic rock, of from fifty to a hundred feet in height, a truly nov- 
el and interesting sight! ‘The rock in particular parts, presented 
somewhat regular columns with small pores, and then irregular masses, 
with pores often of a size to contain many gallons, the whole hay- 
ing a dark burnt aspect, the upper parts presenting a somewhat 
stratified appearance. ‘The next day we travelled in the same di- 
rection over a high barren plain, strewed with volcanic glass and 
sharp broken stones of similar origin, having little other variety in 
-its surface than the deep channels of the streams. 
We continued our journey, for many days, in a leisurely manner, 
and by a zigzag route, but the general course tended 8. W. for a 
direct distance of about four hundred miles, over ridges, and cross- 
ing streams falling into the Lewis River from the 8S. E. 
The atmosphere was still extremely dry, as was indicated by the 
shrinkage of timber and by extreme thirst. Occasionally, a threat- 
ning cloud of small size was formed, attended by thunder, when the 
rain might be seen falling part of the way to the earth, but seldom 
did a drop reach its thirsty surface. ‘The plains, along the creeks, 
were of volcanic rocks, similar to those before described, and most of 
