"On descending the butte to the east of our camp, I found before me another valley, a treeless barren plain, probably ten miles in width. From the far side of this valley butte after butte arose and grouped themselves along the horizon, and looked together in the distance like the huge fortified city of a giant race, the utter desolation of the scene, the dried-up watercourses, the absence of any moving object, the profound silence which prevailed, produced a feeling that was positively oppressive. When I thought of the buttes beneath our feet, with their entombed remains of multitudes of animals for ever extinct, and reflected upon the time when the country teemed with life, I truly felt that I was standing on the wreck of a former world."
These old lake-basins, in which so many forms of life have been sealed up, all lie between the Rocky Mountains on the east, and the Wasatch Range on the west, or along the high central plateau of the continent. As the mountains were slowly elevated, part of the old sea of the Cretaceous period (that sea in which the “sea-serpents” played so important a part) was enclosed and cut off from the ocean. Rivers began to pour their waters into it, so that the waters became less and less salt, until at last a fresh-water lake, or series of lakes, was formed. As the upward movement of this region continued these lakes were all the while receiving sedimentary materials, such as sand and mud, from the rivers, until finally they were filled up, but not until the sediments had formed a mass of strata over a mile in thickness. Thus we see how favourable were the conditions for a faithful record of Eocene life-history.
But another process was going on which helped to bring them to an end; for they were being slowly drained by the rivers that flowed out of them, and these rivers kept on continually deepening their channels, so that we have dry land where the lakes once were. Now the region is over 6000 feet above the sea, and probably more than one-half of these fresh-water deposits have been washed away, mainly through the Colorado River. What is left of the Eocene strata forms the “Bad Lands.” The same geological action that has cut up and carved out this region into buttes, cañons, cliffs, peaks, and columns of fantastic shapes, has also brought to light the extinct animals preserved in the rocks, much in the same way as an old burial-ground, if cut up by intersecting trenches, might be made to yield up the bones of those who for generations had been buried therein.
Professor Marsh first discovered remains of Dinocerata in 1870, while investigating this Eocene lake-basin, which had never before been explored. It was here, also, that he found the wonderful series of fossil horses by means of which he has been able to prove that our modern horse is descended from a small quadruped with five toes, and to show the different stages in its evolution. Here, also, were found old-fashioned types of carnivorous quadrupeds, of rodents, and of insectivorous creatures. But reptiles as well as quadrupeds flourished on the borders of the old lake, for the remains were found of crocodiles, tortoises, lizards, and serpents; its waters, too, were well stocked with fish.
Everything here testifies to a long continuance of those conditions under which plant and animal life can flourish, namely, a warm climate, plenty of food, and freedom from those physical changes which, by altering the geographical features of a country, bring so many important consequences in their train. The geological record tells us that this happy state of things lasted all through the Eocene period, and until the fresh-water lakes had at last been drained away by their outflowing rivers.
In October, 1870, a later Eocene lake-basin was discovered by the same exploring party, and this Professor Marsh calls the Uinta basin, because it was situated south of the Uinta Mountains. “In the attempt to explore it,” he says, “our party endured much hardship, and also were exposed to serious danger, since we had only a small escort of United States soldiers, and the region visited was one of the favourite resorts of the Uinta-Utes. These Indians were then, many of them, insolent and aggressive, and since have been openly hostile, at one time massacring a large body of Government troops sent against them. Two subsequent attempts ... to explore this region met with little success.”
This lower lake was of later (or upper) Eocene age, and the extinct animals preserved in its ancient bed appear to resemble more nearly those of the famous Paris basin, referred to in the beginning of this chapter, than any yet discovered in America. But the basin north of the Uinta Mountains, where alone the Dinocerata had been found, offered so inviting a field that, in the spring of 1871, Professor Marsh began to explore it systematically. He organised an expedition, with an escort of U.S. soldiers, and the work continued during the whole season. In this way a large collection was secured. Explorations were continued in the spring of the following year, which resulted in the discovery of the type specimen of the Dinoceras mirabile. Another expedition was organised in 1873, also with an escort of soldiers, and a great many specimens were collected. These researches were continued during 1874, and again in 1875, with good results. Since then various small parties have been equipped and sent out by Professor Marsh to collect in the same region of the “Bad Lands;” and, finally, during the entire season of 1882, the work was vigorously prosecuted under his direction, and afterwards under the auspices of the United States Geological Survey. This brief account of the difficulties and hardships encountered by Professor Marsh and his companions, for which we are indebted to his exhaustive monograph, will serve to give some idea of the nature of those labours, undertaken in the cause of Science, which he has brought to so successful an issue.
In the country east of the Rocky Mountains, including the states of Dakota, Nebraska, Wyoming, and part of Colorado, Professor Marsh has discovered the remains of yet another strange group of large quadrupeds. The best known of these is Brontops, of which the skeleton is seen in [Fig. 45]. These animals lived after the Dinocerata, namely, in the Miocene period, and were the largest American mammals of that period. They constitute a distinct family more nearly allied to the rhinoceros than to any other living form. The skeleton on which [Fig. 45] is founded was the most complete of any yet discovered by Professor Marsh. Portions of it were exhumed at different times, but it was first found in 1874. Our artist has made the restoration seen in [Plate XV.] from this skeleton, as figured by Professor Marsh.