Ignorant of a ford so near above, the caravan turned down towards the crossing of the former traders. "We travelled fifty miles," {183} says Mr. Stanley, who was of the caravan, "the whole of which distance the river is bound in by cliffs several hundred feet high, in many places nearly perpendicular. We at length came to the termination of the table land; but what scene presented itself! [Pg241] The valley below could only be reached by descending a frightful cliff of from 1200 to 1500 feet, and more or less precipitous. After a search of several hours, a practicable way was found; and, with the greatest fatigue and exertion, by locking wheels, holding on with ropes, and literally lifting the wagons down in places, we finally succeeded in reaching the bottom.... How did the Canadian and other streams in New Mexico sink themselves to such immense depths in the solid rock? It seems impossible that the water should have worn away the rock while as hard as in its present state. What a field of speculation for the geologist, in the propositions--Were the chasms made for the streams, or did the streams make the chasms? Are they not of volcanic origin?" Nor are the flat prairies always free from this kind of annoyance to travellers. They are not unfrequently intersected by diminutive chasms or water-cuts, which, though sometimes hardly a rod in width, are often from fifty to a hundred feet deep. These little cañones are washed out by the rains, in their descent to the bordering streams, which is soon effected after an opening is once made through the surface; for though the clayey {184} foundation is exceedingly firm and hard while dry, it seems the most soluble of earths, and melts almost as rapidly as snow under the action of water. The tenacious turf of the 'buffalo grass,' however, retains the marginal surface, so that the sides are usually perpendicular--indeed, often shelving inward at the base, and therefore utterly impassable. I have come unsuspectingly upon the verge of such a chasm; and though, to a stranger, the appearance would indicate the very head of the ravine, I would sometimes be compelled to follow its meandering course for miles without being able to double its 'breaks.' These I have more especially observed high on the borders of the Canadian. [Pg242] The geological constitution of the Prairies is exceedingly diversified. Along the eastern border, especially towards the north, there is an abundance of limestone, interspersed with sandstone, slate, and many extensive beds of bituminous coal. The coal is particularly abundant in some of the regions bordering the Neosho river; where there are also said to be a few singular bituminous or 'tar springs,' as they are sometimes called by the hunters. There are also many other mineral, and particularly sulphur springs, to be met with.