Geology, &c. of the country west of the Rocky Mountains. 5 
the intervening mountain ridges were composed of the same limestone 
that has already been named; but in one instance, we met with a 
mountain of mica slate and variegated marble, unburnt, while bowlders 
of the same were strewed over the basaltic plains. In another place 
we saw a country, broken into granite peaks, which appeared to have 
undergone the action of fire in different degrees. In some parts, the 
rocks were crumbling into sand, in other places they were vitrified, 
so that the particles of quartz appeared like glass ; again, the whole 
appeared to have been melted so far as to form an impure jasper, 
and again it was transformed into amygdaloid. Often in the streams 
and elsewhere, we found chalcedony and other silicious minerals, ap- 
parently of the same origin. 
Against the American falls, we were in sight of the Lewis river, 
beyond which extended an immense open plain, with a snowy moun- 
tain beyond. There was also snow on some of the mountains about 
us and often frost at night, it being now August; still the temperature 
at noon was from 70° to 80°. It was said, we passed nigh a large 
salt lake on the left, into which, flow several fresh rivers, and from 
which there is no outlet to the ocean, as laid down in maps. And 
why need we suppose an outlet, since we know that similar lakes, 
are similarly situated in the center of other continents? And did 
such an outlet exist would it probably continue salt? The supply 
of aqueous vapor to the atmosphere, in situations remote from the 
ocean, appears insufficient for the promotion of vegetation, and thus 
are producing desert steppes and savannahs, and our own parched 
prairies of this central region. 
The last of August we had reached a country open to the south, 
with the streams flowing that way, and which do not probably join 
the Columbia. Here twelve of us, neither of whom had before been 
west of the Alleganies, bade farewell to our trapping companions, 
with whom we had travelled for mutual protection, from the Black- 
foot Indians, whom we had now passed, but gained nothing on our 
journey as to the distance, to be travelled. 
We now turned our course N. W. and set ourselves to seek our 
Way as it were, by instinct. We soon reached the head waters of a 
creek, by pursuing which in a N. W. direction, about one hun- 
dred miles, we again fell in with the Lewis river. The first part 
of the way was through a broken country, of granite, mica slate, 
clay slate, marble, sparry limestone, (burnt and unburnt,) then over 
a plain of apparently burnt sandstone, broken only by the 
