10th.--We parted with our hospitable host after breakfast the next morning, and reached St. Vrain's fort, about forty-five miles from St. Helena, late in the evening. This post is situated on the South fork of the Platte, immediately under the mountains, about seventeen miles east of Long's peak. It is on the right bank, on the verge of the upland prairie, about forty feet above the river, of which the immediate valley is about six hundred yards wide. The stream is divided into various branches by small islands, among which it runs with a swift current. The bed of the river is sand and gravel, the water very clear, and here may be called a mountain-stream. This region appears to be entirely free from the limestones and marls which give to the Lower Platte its yellow and dirty color. The Black hills lie between the stream and the mountains, whose snowy peaks glitter a few miles beyond. At the fort we found Mr. St. Vrain, who received us with much kindness and hospitality. Maxwell had spent the last two or three years between this post and the village of Taos; and here he was at home, and among his friends. Spaniards frequently came over in search of employment; and several came in shortly after our arrival. They usually obtain about six dollars a month, generally paid to them in goods. They are very useful in a camp, in taking care of horses and mules; and I engaged one, who proved to be an active, laborious man, and was of very considerable service to me. The elevation of the Platte here is five thousand four hundred feet above the sea. The neighboring mountains did not appear to enter far the region of perpetual snow, which was generally confined to the northern side of the peaks. On the southern, I remarked very little. Here it appeared, so far as I could judge in the distance, to descend but a few hundred feet below the summits. I regretted that time did not permit me to visit them; but the proper object of my survey lay among the mountains farther north; and I looked forward to an exploration of their snowy recesses with great pleasure. The piney region of the mountains to the south was enveloped in smoke, and I was informed had been on fire for several months. Pike's peak is said to be visible from this place, about one hundred miles to the southward; but the smoky state of the atmosphere prevented my seeing it. The weather continued overcast during my stay here, so that I failed in determining the latitude, but obtained good observations for the time on the mornings of the 11th and 12th. An assumed latitude of 40 deg. 22' 30" from the evening position of the 12th, enabled me to obtain for a tolerably correct longitude, 105 deg. 12' 12".