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 hunters, and has very much the flavor of Alleghany mountain sheep. I have frequently seen the horns of this animal three feet long and seventeen inches in circumference at the base, weighing eleven pounds. But two or three of these were killed by our party at this place, and of these the horns were small. The use of these horns seems to be to protect the animal's head in pitching down precipices to avoid pursuing wolves--their only safety being in places where they cannot be followed. The bones are very strong and solid, the marrow occupying but a very small portion of the bone in the leg, about the thickness of a rye straw. The hair is short, resembling the winter color of our common deer, which it nearly approaches in size and appearance. Except in the horns, it has no resemblance whatever to the goat. The longitude of this place, resulting from chronometer and lunar distances, and an occultation of Arietis, is 107° 13' 29", and the latitude 42° 33' 27". One of our horses, which had given out, we left to receive strength on the island, intending to take her, perhaps, on our return.