The road led over an interesting plateau between the North fork of the Platte on the right, and Laramie river on the left. At the distance of ten miles from the fort, we entered the sandy bed of a creek, a kind of defile, shaded by precipitous rocks, down which we wound our way for several hundred yards, to a place where, on the left bank, a very large spring gushes with considerable noise and force out of the limestone rock. It is called the "Warm Spring," and furnishes to the hitherto dry bed of the creek a considerable rivulet. On the opposite side, a little below the spring, is a lofty limestone escarpment, partially shaded by a grove of large trees, whose green foliage, in contrast with the whiteness of the rock, renders this a picturesque locality. The rock is fossiliferous, and, so far as I was able to determine the character of the fossils, belongs to the carboniferous limestone of the Missouri river, and is probably the western limit of that formation. Beyond this point I met with no fossils of any description.
I was desirous to visit the Platte near the point where it leaves the Black hills, and therefore followed this stream, for two or three miles, to its mouth, where I encamped on a spot which afforded good grass and _prele (equisetum)_ for our animals. Our tents having been found too thin to protect ourselves and the instruments from the rains, which in this elevated country are attended with cold and unpleasant weather, I had procured from the Indians at Laramie a tolerably large lodge, about eighteen feet in diameter, and twenty feet in height. Such a lodge, when properly pitched, is, from its conical form, almost perfectly secure against the violent winds which are frequent in this region, and, with a fire in the centre, is a dry and warm shelter in bad weather. By raising the lower part, so as to permit the breeze to pass freely, it is converted into a pleasant summer residence, with the extraordinary advantage of being entirely free from musquitoes, one of which I never saw in an Indian lodge. While we were engaged very unskilfully in erecting this, the interpreter, Mr. Bissonette, arrived, accompanied by the Indian and his wife. She laughed at our awkwardness, and offered her assistance, of which we were frequently afterwards obliged to avail our selves, before the men acquired sufficient expertness to pitch it without difficulty. From this place we had a fine view of the gorge where the Platte issues from the Black hills, changing its character abruptly from a mountain stream into a river of the plains. Immediately around us the valley of the stream was tolerably open; and at the distance of a few miles, where the river had cut its way through the hills, was the narrow cleft, on one side of which a lofty precipice of bright red rock rose vertically above the low hills which lay between us.