Saturday 27.  We proceeded on but slowly, the current being still so rapid as to require the utmost exertions of us all to advance, and the men are losing their strength fast in consequence of their constant efforts.  At half a mile we passed an island, and a mile and a quarter further again entered a ridge of hills which now approach the river with cliffs apparently sinking like those of yesterday.  They are composed of a solid limestone of a light lead colour when exposed to the air, though when freshly broken it is of a deep blue, and of an excellent quality and very fine grain.  On these cliffs were numbers of the bighorn.  At two and a half miles we reached the centre of a bend towards the south passing a small island, and at one mile and a quarter beyond this reached about nine in the morning the mouth of a river seventy yards wide, which falls in from the southeast.  Here the country suddenly opens into extensive and beautiful meadows and plains, surrounded on every side with distant and lofty mountains.  Captain Lewis went up this stream for about half a mile, and from the height of a limestone cliff could observe its course about seven miles, and the three forks of the Missouri, of which this river is one.  Its extreme point bore S. 65 degrees E. and during the seven miles it passes through a green extensive meadow of fine grass dividing itself into several streams, the largest passing near the ridge of hills on which he stood.  On the right side of the Missouri a high, wide and extensive plain succeeds to this low meadow which reaches the hills.  In the meadow a large spring rises about a quarter of a mile from this Southeast fork, into which it discharges itself on the right side about four hundred paces from where he stood.  Between the southeast and middle forks a distant range of snow-topped mountains spread from east to south above the irregular broken hills nearer to this spot:  the middle and southwest forks unite at half a mile above the entrance of the southeast fork.  The extreme point at which the former can be seen, bears S. 15 degrees E. and at the distance of fourteen miles, where it turns to the right round the point of a high plain and disappears from the view.  Its low grounds are several miles in width, forming a smooth and beautiful green meadow, and like the southeast fork it divides itself into several streams.  Between these two forks and near their junction with that from the southwest, is a position admirably well calculated for a fort.  It is a limestone rock of an oblong form, rising from the plain perpendicularly to the height of twenty-five feet on three of its sides; the fourth towards the middle fork being a gradual ascent and covered with a fine green sward, as is also the top which is level and contains about two acres.  An extensive plain lies between the middle and southwest forks, the last of which after watering a country like that of the other two branches, disappears about twelve miles off, at a point bearing