The hill which forms the basis of the fort is a dark gray micaceous sandstone in horizontal laminæ, and is elevated about thirty feet above the water. The {36} country back of the fort has an undulating surface, and rises gradually as it recedes, being covered with heavy forests of oak, tulip tree, sassafras, &c. Towards the south and south-east, at no great distance, rise the summits of the mountainous range already mentioned. The Sugar-loaf and Cavaniol mountains (the former being one of a group of these similar conic summits), are visible from some points near Fort Smith. The Poteau, so called by the French from the word signifying a post or station, rises sixty or seventy miles south of Belle Point, opposite to the sources of the Kiamesha, a branch of Red river. Nearly the whole of its course is through a hilly or mountainous region, but it is one so sparingly supplied with water, that the Poteau, within two miles of its confluence with the Arkansa, is in the dry season no more than a trifling brook. In an excursion which we made from Fort Smith, we ascended the Poteau about a mile and a half, where we observed an extensive bed of bituminous clay-slate, indicating the neighbourhood of coal. Tracing this slate to the south and east, we found it to pass under a very considerable sandstone hill. Several circumstances induce us to believe that it is also underlayed by a sandstone similar to that at the fort. Attentive examination will show that these rocks have a slight inclination towards the east; and if the bituminous slate in question had been underlayed by compact limestone, as has been conjectured,[92] it is highly probable this rock would have emerged near where the sandstone appears at Belle Point. We make this remark because, although we have often seen both limestone and bituminous clay-slate in various parts of the Arkansa territory, it has never been our fortune to meet with them in connexion. A few rods above this bed of bituminous slate we crossed the Poteau almost at a single step, and without wetting the soles {37} of our mockasins, so inconsiderable was the quantity of water it contained. The point between the confluence of the Poteau and the Arkansa is low and fertile bottom land, and, like that on the opposite side of the river, covered with dense and heavy forests of cotton-wood, sycamore, and ash, intermixed with extensive and impenetrable cane brakes. In these low grounds the beautiful papaw tree, whose luscious fruit was now ripe, occurs in great abundance. It rises to the height of thirty or forty feet, and its trunk is sometimes not less than a foot in diameter.