It was my immediate conclusion, and one that would be promptly formed by any other superficial observer, that this shell-bearing stratum had some time been the bed of a prehistoric body of water, which existed there previous to the upheaval of all that territory, covering all of what is now known as the Bad Lands. I observed also that the level strata in the distant bluffs were each a duplicate of the strata in all the others. It suggested at once the age when they were continuous, and the fact that I was now standing, not on a mountain summit, but on what was once the common level of that country. Surely the continuous action of the elements, beginning perhaps with the wearing out of the gullies near the river, had worn back into the high plain and gradually widened out in all directions until nothing remained of the original level, except these few high elevations. Scott's Bluff, Chimney Rock, Castle Rock, and other notable peaks alone remain to tell their tale of the ages that have passed since this work of erosion began. This, however, is but part of the story discovered in the descent. The perpendicular faces of the bluff present three or four varieties of clay formation, slight differences in color and texture being noticeable. One series of strata, called Mortar beds in Darton's geological reports, is called the Ogalalla formation, the strata being merged into a light colored, sandy clay. Beneath this is a formation sufficiently lithyfied to be fairly classed as soft sandstone, and beneath it all, as late examination shows, the Pierre clay, now supposed to be at least 2,000 feet in thickness at this point. Here also is seen at a glance one of the great sources of the enormous volume of sediment continually borne along in the waters of the Platte and down the great Missouri River, which have transported many cubic miles of earth and have deposited it to form the alluvial lands now forming the great states along the waters of the lower Mississippi. The suggestion seems overpowering, but true it is, that by these slow processes extending through ages, immeasurable even by the most learned geologist, the surface of this part of our continent has been transformed without limit. I had carefully inspected the surfaces of the bluffs and the interesting panorama that surrounded them; the next problem was to descend. This would have been simple enough if I had been content to retrace my steps and return by the ravine I had followed in ascending, but I had crossed to the southern rim of the summit, and I desired to explore that side of the eminence. On the southwest corner, however, there appeared to be a dry run which from my point of observation seemed to afford a safe and comparatively unbroken descent to the foot of the cliffs on that side. Although the view looking down this newly discovered ravine was not so comprehensive in all its details as would have been obtained below at a distance, I nevertheless determined to risk it.