September 2.  It rained last night, and this morning we had a high wind from the N.W.  We went three miles to the lower part of an ancient fortification on the south side, and passed the head of Bonhomme island, which is large and well timbered:  after this the wind became so violent, attended by a cold rain, that we were compelled to land at four miles on the northern side, under a high bluff of yellow clay, about one hundred and ten feet in height.  Our hunters supplied us with four elk; and we had grapes and plums on the banks:  we also saw the beargrass and rue, on the side of the bluffs.  At this place there are highlands on both sides of the river which become more level at some distance back, and contain but few streams of water.  On the southern bank, during this day, the grounds have not been so elevated.  Captain Clarke crossed the river to examine the remains of the fortification we had just passed.

[Illustration:  Fortification]

This interesting object is on the south side of the Missouri, opposite the upper extremity of Bonhomme island, and in a low level plain, the hills being three miles from the river.  It begins by a wall composed of earth, rising immediately from the bank of the river and running in a direct course S. 76 degrees, W. ninety six yards; the base of this wall or mound is seventy-five feet, and its height about eight.  It then diverges in a course S. 84 degrees W. and continues at the same height and depth to the distance of fifty-three yards, the angle being formed by a sloping descent; at the junction of these two is an appearance of a hornwork of the same height with the first angle:  the same wall then pursues a course N. 69 degrees W. for three hundred yards:  near its western extremity is an opening or gateway at right angles to the wall, and projecting inwards; this gateway is defended by two nearly semicircular walls placed before it, lower than the large walls; and from the gateway there seems to have been a covered way communicating with the interval between these two walls:  westward of the gate, the wall becomes much larger, being about one hundred and five feet at its base, and twelve feet high:  at the end of this high ground the wall extends for fifty-six yards on a course N. 32 degrees W; it then turns N. 23 degrees W. for seventy-three yards:  these two walls seems to have had a double or covered way; they are from ten to fifteen feet eight inches in height, and from seventy-five to one hundred and five feet in width at the base; the descent inwards being steep, whilst outwards it forms a sort of glacis.  At the distance of seventy-three yards, the wall ends abruptly at a large hollow place much lower than the general level of the plain, and from which is some indication of a covered way to the water.  The space between them is occupied by several mounds scattered promiscuously through the gorge, in the centre of which is a deep round hole.  From the extremity of the last wall, in a course N. 32 degrees W. is a distance