Thursday 13.  They left their encampment at sunrise, and ascending the river hills went for six miles in a course generally southwest, over a country which though more waving than that of yesterday may still be considered level.  At the extremity of this course they overlooked a most beautiful plain, where were infinitely more buffaloe than we had ever before seen at a single view.  To the southwest arose from the plain two mountains of a singular appearance and more like ramparts of high fortifications than works of nature.  They are square figures with sides rising perpendicularly to the height of two hundred and fifty feet, formed of yellow clay, and the tops seemed to be level plains.  Finding that the river here bore considerably to the south, and fearful of passing the falls before reaching the Rocky mountains, they now changed their course to the south, and leaving those insulated hills to the right proceeded across the plain.  In this direction captain Lewis had gone about two miles when his ears were saluted with the agreeable sound of a fall of water, and as he advanced a spray which seemed driven by the high southwest wind arose above the plain like a column of smoke and vanished in an instant.  Towards this point he directed his steps, and the noise increasing as he approached soon became too tremendous to be mistaken for any thing but the great falls of the Missouri.  Having travelled seven miles after first hearing the sound he reached the falls about twelve o’clock, the hills as he approached were difficult of access and two hundred feet high:  down these he hurried with impatience and seating himself on some rocks under the centre of the falls, enjoyed the sublime spectacle of this stupendous object which has since the creation had been lavishing its magnificence upon the desert, unknown to civilization.

[Illustration:  The Falls and Portage]

The river immediately at its cascade is three hundred yards wide, and is pressed in by a perpendicular cliff on the left, which rises to about one hundred feet and extends up the stream for a mile; on the right the bluff is also perpendicular for three hundred yards above the falls.  For ninety or a hundred yards from the left cliff, the water falls in one smooth even sheet, over a precipice of at least eighty feet.  The remaining part of the river precipitates itself with a more rapid current, but being received as it falls by the irregular and somewhat projecting rocks below, forms a splendid prospect of perfectly white foam two hundred yards in length, and eighty in perpendicular elevation.  This spray is dissipated into a thousand shapes, sometimes flying up in columns of fifteen or twenty feet, which are then oppressed by larger masses of the white foam, on all which the sun impresses the brightest colours of the rainbow.  As it rises from the fall it beats with fury against a ledge of rocks which extend across the river at one hundred and fifty yards from the precipice.  From