Two years later, in 1884, I was employed by the late Professor Marsh to explore this same fossil bed. The bones which I was after now were covered by fourteen feet of moulding sand and a four-foot ledge of hard rock, the heavier bones lying on the sandstone, the lighter ones mingled with the sand above. This sand and rock had to be removed by pick and scraper, which meant that there was a large amount of heavy labor before us. Therefore, having more means at my command than I had had before, I drove up to Mr. Overton’s door and offered him forty dollars a month to work for us with his team during the whole summer, with the understanding that I was to have all the fossils found. This offer he gladly accepted, and I found him a very careful worker. Not only did he do the rough work well, but when we got a floor laid bare above the bones, he proved to be a most careful collector. My other assistant on this expedition was a Mr. Will Russ, who afterwards became a skilful dentist.
Our method of work was first to cut down and remove the sand and rock for a space twenty feet wide and perhaps a hundred long, using a plow and scraper. Then we cleaned up our floor and uncovered the bones with oyster knives and other tools which we had made to suit our purpose. One, I remember, was a hoe straightened out at the shank and cut off at the corners to make a diamond-shaped tool. With this we could work under the high bank, and take out specimens which we could not reach otherwise. Trowels and diggers of various patterns were used also.
The bones which we were collecting lay scattered along both sides of the ravine for a quarter of a mile, often in pockets or pot-holes in the gray sandstone. Of this there are two layers, about fourteen feet apart, the interspace being filled with beds of fine moulding sand, with some whiting from the underlying chalk, which constituted the land surface when these fresh-water beds were deposited. There are also beds of sand that have been washed clean by the currents of the flood-plain of some ancient river, for the exposed section shows all the different deposits of an overflowed valley. Above the washed sand is a stratum of sand and clay, indicating that here was a quiet place where the muddy backwater deposited its load. This layer, upon exposure, cracks in all directions, like the mud at the bottom of a puddle after the water has evaporated.
It has always been a problem to account for the number of the animals represented here, and for the fact that the bones are so scattered. All parts of the skeletons are mingled in the greatest confusion, with no two bones in a natural position. One is, of course, forced, after an observation of this country, to agree with Drs. Matthew and Hatcher that these bones were deposited in the flood-plain of a running stream and not in great lakes, as was believed by older geologists. But the only supposition upon which I can account for the intermingling of all the bones of the skeletons on the bottom sandstone layer is that the fine sand through which the bones were distributed, becoming saturated with water, was converted into a quicksand, in which the bones sank until they reached the impenetrable layer below; the heavier bones of course being at the bottom.
What caused the death of the countless individuals in the Sternberg Quarry, is a question not easily answered. The authorities quoted above believe that during the Upper Miocene Period, there were many water-courses separated, by slightly elevated divides and broad flood-plains, with possibly here and there small lakes, where the dense vegetation had clogged some sluggish stream. But during a rainy season of unusual duration, the whole region for many miles must have been converted into a series of lakes; and all the animals in the vicinity, after having gathered at the highest points they could find to escape death, must have been finally overwhelmed by some great flood that covered every inch of ground. Then after maceration took place, the bones might have been scattered by other floods.
A theory of my own, equally plausible, is that the animals were buried beneath a sandstorm, which tore loose the fine sand of the flood-plain, and scattered it in suffocating volumes over the frightened multitudes which had herded together in search of safety or courage.
This land, now three thousand feet above sea level, was only a few feet above when these rhinoceroses moved over it in countless herds. Everywhere were swamps filled with sponge moss, and tropical streams, whose wealth of vegetation formed thick jungles along their banks. On firmer ground, great areas were covered with a dense growth of rushes, through which the paths of these animals were the only trails; while higher up still, the soft damp soil gave a foothold to forests, through which the great mastodons sounded their trumpet calls, as they roamed about, tearing up trees with their powerful trunks and feasting upon the rich, juicy roots.
Fig. 24.—Three-toed Horse, Hypohippus.
From the Middle Eocene of Colorado. (After Gidley.) In American Museum of Natural History.
