65 
the 2d of August, the expedition passed in a north-westerly 
direction, im sight of British Territory, touched the banks 
of the Mouse River, a tributary of the Assineboine, and 
thence southerly to Fort Berthold, from where it turned its 
face to the point of starting. 
The valley of the upper Missouri is bounded on both sides 
by table lands, which rise from the alluvial plain, in many 
places very abruptly and often to heights of probably from 
300 to 800 feet, giving to the country, as seen from the 
banks of the river, here and there quite a mountainous 
aspect. It is only when the explorer has ascended the sides 
of this trough, that he is undeceived by seeing the approxi- 
mate levels of a great plateau spreading before him, broken, 
only now and then by water courses or capped by hills, 
whose, occasionally flat, heads remain as monuments of 
another higher plateau, now almost entirely gone. 
The table-land to the west of the Missouri Valley forms 
an inclined plain, which rises gently from the border of the 
trough rim, apparently attaining its greatest elevation in the 
immediate vicinity of the Little Missouri des Gros Ventres, 
or between this stream and the Yellowstone, and is intersect- 
ed by two systems of watercourses, the streams of one of 
which, flow, generally speaking, from west to east and enter 
the Missouri below Fort Berthold, while those of the other 
system pursue a direction from south to north and join the 
great Water-Artery of the country above the point men- 
tioned. ‘The action of the streams of the first system on the 
physical outlines of the country has generally been but slight, 
that of those of the second system at times very powerful. 
The contrast between the resulting effects, leaves a very 
vivid impression in the mind of the observer, who pursues 
the route of the expedition of 1864. Following the courses 
of the Cannonball and Heart Rivers, the eye is met every- 
where by the same gently undulating plain, in which the 
river valleys form but slight indentations, and above which 
the ridge of the Takaokutah Mountains rises in the North, 
to an elevation of perhaps from 800 to 1000 feet. About 
three hundred miles of this plain, may have been traversed 
