It was thought advisable to make some addition to our force at Isle au Vache, as we should soon be in advance of the troops on the Missouri, and might be exposed to insults and depredations, from some of the numerous tribes of Indians. Accordingly, on application to Colonel Morgan, a boat and fifteen men, under the command of Lieutenant Fields, were detailed for this duty, and directed to regulate their movements agreeably to the orders of the commanding officer of the exploring expedition.[146] These men were furnished with provisions for sixty days, and having embarked on board a keel-boat, called the General Smith, they sailed in company with the Western Engineer. A favourable wind springing up, we proceeded in the course of the day about twenty-three miles, and encamped at night near the entrance of a small stream, called Independence Creek. A little above, and on the south side of the river, is the site of an old Konza town, formerly called the village of the Twenty-four.[147] Above Cow Island the Missouri is more serpentine in direction than below, and the difficulties of the navigation we found by no means diminished as we ascended. The bed of the river in many places is broad, and the water distributed into small channels separated by sand-bars. About fifty miles above Cow Island we passed a spot that had lately been occupied as a hunting camp by Captain Martin, who had been here to procure the requisite provisions for the subsistence of his party. At the Yellow Banks we found the bluffs elevated about one hundred and fifty feet above the surface of the valley.[148] Barometric observations, several times repeated, gave nearly the same result at some points below. One hundred and fifty feet may, therefore, be assumed as the medium depth of the immediate valley of the Missouri; its aggregate width, for the {106} first five hundred miles above the Mississippi, may be estimated at about three miles. The corresponding appearances in the strata of the opposite sides of this valley, as well as its entire form and character, indicate it to have been formed by the river. But far more than that vast body of soil and of rocky strata, which formerly filled the space now occupied by the immediate valley of the river, has been removed by the Missouri. From the summit of the bluffs there is a sloping ascent towards the interior of the country; and it is probable the aggregate elevation of the great plains is not less than three hundred feet above the surface of the river. If we admit that this great valley, with its numerous ramifications, has resulted from the operation of currents, wearing down and transporting to the ocean the solid materials of the earth's surface, it would appear necessary still farther to acknowledge that this channel was once much deeper than at present, for we usually meet with thick alluvial depositions covering the rocks that line the bottom of the Missouri valley. The manifest tendency