BEAVER CANALS, MEADOWS, AND TRAILS. 211 



their area. They form a narrow belt along this por- 

 tion of the Missouri, from which they stretch south- 

 ward across the Yellowstone, and terminate in the 

 Black Hills in the central part of Nebraska. 



About one hundred miles from the foot of the 

 Rocky Mountains we find the most remarkable forma- 

 tion upon the river, and the most striking scenery 

 upon its borders. Lewis and Clark, who passed 

 through this region in 1805, called this formation the 

 "White Walis" — a not inapt designation. Prince 

 Maximilian, in his "Travels in North America," also 

 describes them; but any description, however minute, 

 must fail to convey more than a faint general impres- 

 sion of their actual appearance. They are continuous 

 for about forty miles, first appearing as the north 

 bluff of the river, then upon both sides, and afterward 

 on the north side alone. The river cuts through the 

 formation, which is a whitish friable sandstone, so 

 slightly cemented that small pieces are readily pul- 

 verized with the fingers, and yet it retains the form 

 of solid rock. Its opposite bluffs here approach within 

 half a mile of each other; and rising about two hun- 

 dred feet high, are buried but a few feet below the 

 level surface of the prairie. The extraordinary ap- 

 pearances of these "walls" are the effects, in a great 

 measure, of frost and rain, which, having disinte- 

 grated portions of the rock, have wrought out the 

 marvelous results presented to the eye. A steep bank 

 first rises from the river, which is composed of the 

 comminuted materials of this rock, colored a dingy 

 brown by washings from the soil above. This, ascend- 

 ing about a hundred and fifty feet, at an angle of 60° 

 or more, is destitute of vegetation, and has a smooth, 



