Laramie to where I found it superposed on the granite of the Rocky
mountains, in longitude 109 deg. 00'. From its appearance, the main chain of
the Laramie mountain is composed of this rock; and in a number of places I
found isolated hills, which served to mark a former level which had been
probably swept away.

These conglomerates are very friable, and easily decomposed; and I am
inclined to think this formation is the source from which was derived the
great deposite of sand and gravel which forms the surface rock of the
prairie country west of the Mississippi.

Crossing the ridge of red sandstone, and traversing the little prairie
which lies to the southward of it, we made in the afternoon an excursion
to a place which we called the Hot Spring Gate. This place has much the
appearance of a gate, by which the Platte passes through a ridge composed
of a white and calcareous sandstone. The length of the passage is about
four hundred yards, with a smooth green prairie on either side. Through
this place, the stream flows with a quiet current, unbroken by any rapid,
and is about seventy yards wide between the walls, which rise
perpendicularly from the water. To that on the right bank, which is the
lower, the barometer gave a height of three hundred and sixty feet. This
place will be more particularly described hereafter, as we passed through
it on our return.

We saw here numerous herds of mountain sheep, and frequently heard the
volley of rattling stones which accompanied their rapid descent down the
steep hills. This was the first place at which we had killed any of these
animals; and, in consequence of this circumstance, and of the abundance of
these sheep or goats, (for they are called by each name,) we gave our
encampment the name of Goat Island. Their flesh is much esteemed by the