The beds of coal in this district lie horizontally, varying much in thickness, and occurring often at an elevation of a few feet above the surface of the water in the Missouri.[126] On the first of August we arrived at Fort Osage, one hundred and five miles above the mouth of Grand river. Here Mr. Say and his party had been some days encamped, having arrived on the 24th of July from their equestrian journey across the country from Franklin. After leaving that place on the 19th, they passed through a fine bottom on the left side of the river, closely covered with forests of oaks, elms, hackberry, walnut, the mulberry, the gleditschia, the guilandina, and the other trees common on the Missouri, for twelve miles, when they arrived at Arrow rock, where is a ferry by which they crossed {93} the Missouri. In this walk they passed a field of corn, containing seven hundred acres. The ferry boat used at Arrow rock is one peculiarly adapted to the navigation of a rapid stream. It consists of two canoes, on which rests a platform, with a slight railing to prevent cattle from falling off. Arrow rock is so called from its having been formerly resorted to, by the neighbouring Indians, for the stone used to point their arrows. It is a beautiful situation, and rises to considerable elevation above the water.[127] From its summit is a pleasing view of the river, and near the base is a remarkable eddy, which, as they were crossing, whirled their ferry-boat entirely round. On the second day they left their encampment at an early hour, and travelled forward through plains where very few trees were to be seen. They turned off from the Osage trace, in which they had been travelling, and went eight miles to visit the salt-works, and some remarkable diggings, on the saline fork of the Le Mine. Here, at one establishment, one hundred bushels of salt are manufactured per week; eight men are employed, and one hundred and eighty gallons of water are evaporated to produce a bushel of salt.[128] Two miles from the confluence of the Camp Fork with the Saline, are the salt-works, and the residence of Mr. Lockhart, who received the detachment with much hospitality.