Produced by Gary Martens and Laurie Saikin
This group was originally called the Lignitic by Meek and Hayden. Small patches of this group are found in the southwestern portion of the State, in Hitchcock County. The Pliocene beds overlie it, but in a few places close to the west line of the State it is exposed. Except this portion, the whole of the State continued to be a land surface through this epoch. The Laramie Sea extended from Southwest Nebraska over the entire plain region of Colorado. It covered a vast expanse of country in New Mexico, Wyoming, Dakota Territory, etc. The rock of the group in Nebraska are mainly composed of sand stones, shales and clays. It is the great coal-bearing group of the West. The coal is most nearly allied chemically to the lignitic series. The animal remains of this group show that it was principally a brackish water deposit. The exact geological position of this group has occasioned much controversy among distinguished scientific men. The weight of testimony and opinion assigns to it a position between the cretaceous and tertiary ages. In other words, it is a transition group. Its vegetable remains are distinctly tertiary; its reptilian life was cretaceous; its molluscan life was intermediate, the forms being principally brackish water species. This transition group is absent in the Old World. It is a lost chapter in geological history which has been recovered in America. The thickness of the Laramie in Nebraska ranges from twelve to one hundred and twenty feet. Beyond Nebraska it frequently is found to be from 300 to 5,000 feet thick.
Coal in the Cretaceous of Nebraska.--All the various groups of the cretaceous rocks contain coal in places in the Rocky Mountains. The beds range from a few feet to fifteen or more feet in thickness. This has given rise to the hope that coal would be found in workable quantity in the equivalents of these groups in Nebraska. Thus far, this hope has not been realized. Thin beds of lignite have indeed been found from six to eighteen inches thick, but the opening and working of these beds have been attended by constant disappointment, The quality has been inferior and the thickness of the beds insufficient. What the future will bring forth in the way of additional discovery, time alone can tell. In regard to the Laramie group, there is no question, as the coal-producing energies of nature through the cretaceous culminated here. In this respect it is alone inferior to the carboniferous. The thickness of the Laramie group coal beds range from ten to sixty feet.
With the close of the Laramie epoch, the whole series of conformable strata, which had commenced with the Dakota groups, ceased. When the last sediments of the Laramie group had been laid down, there occurred one of the great geological revolutions in the history of the globe. From the eastern base of the mountains to the Wasatch, the whole, region was thrown into a series of folds and undulations. The Uinta Range, with its broad, flat anticlinal, was made at this time. The whole chain of the Rocky Mountains was lifted up so as to leave a broad depression eastward of the Wasatch and on both sides of the Uintas.--(King.) The Laramie group was turned up at all angles, from a few degrees to a vertical position, as it is now found in many places beneath the super incumbent tertiary, This up turning affected also the Cascade Range, which was then first outlined. The whole region of the plains sympathized with this movement, so that the land surface condition of Nebraska, which was commenced in the middle Fort Pierre epoch, was completed and perpetuated far into the tertiary. The elevation in the mountains became sufficient to give free drainage to the sea and exclude the oceanic waters. The great interior sea became so completely exterminated, and the continent so elevated, that it has never since been subjected to the sway of the ocean. Henceforward, fresh water lakes became dominant, down to the borders of our own times.
The culmination of those physical changes that had been in progress during the whole of the latter portion of the cretaceous period inaugurated the Cenozoic age. The cretaceous period came to a close by a very gradual uplift, not of single mountain masses or chains, but by the folding of the entire Rocky Mountain chain, accompanied by the elevation of the whole western portion or half of the continent.
The emergence of the continent was most complete toward the north. The great American Mediterranean Sea, which from the middle cretaceous period had extended from the Wasatch to the meridian of Eastern Nebraska and Middle Kansas, had separated the continent into two elongated bodies of American land. This great sea had now become virtually extinct by the continued continental uprising, thus "giving free drainage to the sea, except along a basin-like depression extending from the Wasatch Range eastward to the meridian of 107°30´, with a north and south extension not yet definitely known. This depression was immediately occupied by an early Eocene lake, whose northern portion corresponded with approximate accuracy to the present drainage basin of Green River. Southward it extended through portions of Utah, New Mexico, Colorado, and probably Arizona."--(Clarence King)
This emergence toward the north, and on the west side of the continent, the greater elevation of its mass and the retreat of the seas, necessarily produced great changes of climate. The mean temperature had gradually become lower and the extremes greater. The climate also became drier. And yet it was warmer and moister than at present, as is evident from the vegetable and animal life of the time. All the old cretaceous forms had disappeared, or had been, by changes of environment, transformed into their modern representatives. Thus was inaugurated the Cenozoic age.
The Cenozoic era, or age of mammals, comprises two periods, namely: First, the Tertiary; second, the Quaternary.
The three divisions of the Tertiary, namely, the Eocene, Miocene and Pliocene, are all represented in the West, but only the two latter in Nebraska.
Eocene Epoch.--As stated above, there are no deposits of this epoch in Nebraska. It has already been explained how Nebraska, during this epoch, continued to be a land surface. The forces that had gradually lifted the continent from the embrace of the sea had left a depression eastward of the Wasatch, which was filled by the waters of the great lake already referred to. Here 10,000 feet of sediments were deposited during the progress of this epoch. Many of these sediments were also of a character that accumulate with extreme slowness. Their original thickness must have been much greater, as a large part of their upper beds have been removed by erosion. Eminent geologists have estimated that at least half a million of years was employed in this work. King has recognized four distinct groups of the Eocene, each of which was characterized by its own peculiar vegetable and animal life. We refer to the life of that time, as it will give us some conception of the condition of nature in Nebraska during those times.
Vegetable Life.--From the lowest or vermilion group, Lesquereux has described forty-six species of plants. Among these were the following: Giant cedars, cotton woods, alders, birch, oaks, figs, magnolias and walnuts. Some of the above species, it will be observed, are characteristic of much warmer climates than now obtain in the same latitudes.
Animal Life.--The Tertiary is remarkable as the age of mammals. The mammalian life of this first epoch--Vermilion group--of the Eocene is its most wonderful feature. Mammals of high type suddenly made their appearance. Though highly generalized compared with their modern representatives, the transition forms connecting them with the animals of the preceding cretaceous period are, if they ever existed, as yet unknown. If the period of transformation was the preceding Laramie group epoch, which is the transition group between the cretaceous and tertiary, then the evolution of their forms occurred elsewhere, where no records of the change have been preserved. It probably, however, was near by, and may have been the plain region of Kansas and Nebraska, and if so, during the early Eocene they came by migration around the shores of the Vermilion Lake, in whose sediments their remains were entombed and preserved.
The distinguishing peculiarity of the mammals that now appeared in large numbers was a certain tapiroid feature that marked them all. They were mostly odd-toed, like most birds and dinosaurs. These latter, in their organization, had some mammalian features in the character of their sacrum, vertebrae, etc., but were still more closely allied to birds, so that it is uncertain of many of them whether they were more reptile or bird. Many eminent zoologists, therefore, believe that some time along the transition periods of the Mesozoic, the dinosaurian branch divided, one part developing into birds and the other into the mammalia. Among these lower Eocene mammals, Cope has described three species of tapiroid carnivora. Of the hoofed animal six species belong to the famous dawn horse family, some of which were not larger then a fox, and had three toes on the hind feet and five on the front feet, four of which were serviceable. another large family here found are called coryphodons. They had a highly generalized type of foot and tooth structure, and were related anatomically to both tapirs and bears. One species was as large as a small elephant.
We must pass over the Green River group of the Eocene, whose sediments are so remarkable for the presence in them of great numbers of fishes and the remains of the most perfect forms of insects. It was during this epoch that the sea several times again temporarily invaded this great Eocene lake.
In the next group of the Eocene, known as the Fort Bridger group, the sediments are composed of buff and gray marls and clays, intercalated between which are beds of green earth. In these deposits are found preserved still more wonderful animal remains. Tapiroid forms were still most abundant. Here flourished one of the most curious mammalian forms of all geological history. The family is called dinocerata by Marsh, and eobasilidae by Cope. This family was first, however, made known by Leidy, by his description of an animal which he called Uintathenium. These animals, of which there were many species, had elongated heads, with three pairs of horns, short legs, and bulky, elephantine bodies. There were other families closely allied to the above, many species of insect-eating mammals, and many other forms. Among these animals of curious structure there flourished eight species of monkeys and many carnivora.
The Unita group epoch was the closing member of the Eocene. Its rock memorials are only found south of the Uinta Mountains, having probably been removed elsewhere by erosion. The old Eocene lake beds have been filling up and rising during the latter portions of their history, and their final extinction closed this period.
The causes that brought the Miocene epoch into existence were gradual in their operation. The land surface of the plains during the Eocene was made up of the eroded materials of the cretaceous, permian and carboniferous rocks. There was free drainage to the sea, but of the rivers and their tributaries of that time we know nothing. The upward movement of the plateau that eventually drained the old Eocene lakes was accompanied by a subsidence of portions of the adjoining plains. The old mountain lakes were shifted eastward, the depressions in the plains making room for them. While the mountains went upward, the plains went downward, like the changing waves of the sea. As this movement was slow, and in progress ages before it was consummated, the probabilities are that the great Miocene Lake of the plains commenced to form before Uinta Lake had terminated its history. There were probably no great convulsive throbs of the earth's crust separating sharply the two epochs. The Eocene shaded into the Miocene epoch. This lake of the plains extended from near the north line of Kansas across Nebraska, a large part of Dakota Territory, west of the Black Hills, and northward to Manitoba. Its exact geographical extent has not been ascertained in Nebraska, owing to the superincumbent Pliocene, which overlaps it, and through which it only projects at intervals. The best exposures in Nebraska commence on the Niobrara River, about three hundred miles west of the mouth of the Keya Paha or Turtle Hill River, and extend to the west line of the State, taking in the White Earth River region and the space between the latter and the north line of the State. It is finely represented on and north of the latter river in Dakota Territory, constituting there a portion of the famous Ma-koo-si-tcha or Mauvais Terre of the French, which has been rendered into English by the term Bad Lands, although in the Dakota tongue it means simply a country hard to travel over. On the west, the Miocene abuts against the undulating surface of the Laramie Group, and therefore did not extend quite to the foot-hills of the Colorado Range. The extent of this great fresh-water lake has been variously estimated at from 100,000 to 130,000 and upward of square miles.
Other equally great lakes were formed west of the Wasatch, and in Oregon, Nevada and Colorado. The foldings of the earth's crust had resulted in forming basins more rapidly than erosion could cut down their outlets, and hence the great number of these fresh-water Miocene lakes. No other geological epoch contained such a number and such large basins of fresh water. Hayden, who first studied the Miocene in Nebraska, called it here the White Earth River group, as the, developments along that stream, which was then included in Nebraska, were specially extensive and remarkable.
Kinds of Rock.--The materials of these Miocene beds vary a great deal in character. This would naturally be expected in a lake bed which received the drainage, through countless ages, of the rivers that now have their outlet through the Missouri. Varying currents and other conditions would naturally frequently change the character of the sediments deposited on the bottom. The rocks that supplied the materials that were carried into this Miocene lake evidently came from the Archaean nucleus of the Rocky Mountains and the Black Hills, the paleozoic, the juro-trias and the different groups of the cretaceous. The eroded materials going seaward were stopped in those old lake beds. Erosion, however, through the Miocene, was by no means as rapid as at present. The height of the plateau region was much less than at present; the atmosphere was moister, the rainfall much gentler and more constant, and a warm, temperate climate obtained. The extreme cold of winter, which is such a mighty agent in the disintegration of rock, and which now characterizes these regions, did not then exist. Hill, valley, plain, mountain and plateau were also covered by dense growths, in places, of grasses, and in places of mighty forests, which protected the land from the denuding agencies which are now constantly at work. The extreme thickness of the Miocene is reached on the west in Oregon, where beds 5,000 feet in vertical thickness are found. On the plains, these beds are comparatively thin. Meek estimated their thickness at from 530 to 600 feet. Where I measured them, on the Upper Niobrara, they rarely exceeded 400 feet. If we calculate the length of Miocene times on the same principle as Eocene, this epoch must have been at least a quarter of a million years long.
On and north of the White Earth, and on the Upper Niobrara, the rocks of the Miocene have the following character: Indurated grit of a reddish brown color, with occasional layers of concretions of silicate of lime, often shading into, first, a coarse, and then a fine green sandstone. Above this occur, sometimes, immense masses of conglomerates, with occasional layers of tabular limestone. Coarse-grained, friable, compact and heavy bedded limestone follow. Limestone layers follow for several miles, often changing into silicious limestone, then sandstone and conglomerate, or the opposite.
While Northwestern Nebraska was a lake bed during these times, the balance of the State continued to be a dry land surface. Where the eastern shore line extended has not yet been made out, owing to the presence of the overlying Pliocene Tertiary.
Life of Miocene Times--Flora.--Among the vegetable forms which I have identified from the Miocene of Northwestern Nebraska were cottonwoods, willows, magnolias, oaks, sassafras, cypress, palms, figs, lindens, maples and pines. Not the least remarkable were sequoias, of which family the giant cedars of California are a lingering remnant. These tree remains have also been detected in the Miocene deposits westward to the Pacific. In fact, these sequoia were the great forest trees all over Northern America and Europe, and even, according to Heer, in Greenland and Iceland all through Miocene times. In Nebraska there must have been extensive forests of these noble trees, as well as palms and figs. The general facies of the vegetation was very warm, temperate or semi-tropical.
Animal Life.--Along with this warm temperate flora there flourished a still more wonderful animal life. It is doubtful whether the conditions for mammalian life were ever so favorable as during this epoch Only a few families can here be noticed. The horse family, which is now represented by one genus, whose characteristic species are the common horse and the ass, was exceptionally rich in genera and species during the Miocene. One of these genera was the anchitherium. It had three toes, all of which touched the ground. The Hyperions also had three toes, but only the middle one was used in walking, the two lateral ones swinging, much like the two side toes of the hog. Merychippus was much like the last. These Miocene horses ranged in size from an animal much smaller then the ass to one as large as the modern horse. At least four genera existed here, and very many species. They roamed around these old lake shores in countless numbers. The titanotheriums which Leidy described were so abundant that their remains at one horizon of the Miocene have given their name to the beds. These animals, semi-aquatic in character, had the bulk of body of elephants. Equally gigantic were the brontotheriums of Marsh, the symboradons of Cope, and magaceratops of Leidy. They united more or less some of the characters of the elephant and the rhinoceros, with distinct affinities for the dinocerata of the Eocene. The head was elongated, with a depression in the middle, giving some resemblance to a pack-saddle. They probably had a small trunk, about as long as that of the tapirs. They had two pairs of horns, one pair being above the nasals and another pair above the eyes, the hind pair being powerful weapons of defense. They probably were the successorsof the dinocerata of the Eocene. Of the symborodons, Cope has described five species. As two species of brontotherinm were also described by Marsh, it is clear that the number of species was great, and, judging from the remains, there must have been a very great number of individuals.
Elephants and mastodons were also already represented by several species. A rhinoceros discovered here was three-fourths the size of the one now living in India. The European tertiary river-horse, hyopotamus, was represented here by one species. The camel family also made its appearance here during this epoch, by several genera and many species, some of which were of large size.
No family of animals was represented in that epoch by more genera, species and individuals than the oreontidae. Leidy, who first described them, called them ruminating hogs. The skull approached more nearly to that of the peccaries, though the upper part had some characters uniting them with the camels. The molars were like those of ruminants, and resembled most nearly those of the deer, but, unlike modern muninants, they had incisors in both jaws. The canines resembled most nearly those of the hog. The teeth, as a whole, formed an almost unbroken arch, a condition found in few animals besides the quadruanna. Like the hogs, too, they had four toes on each foot, two being functional, and the two on the sides being too elevated to touch the ground. They were therefore emphatically what Leidy called them--ruminating hogs. They were, judging from the abundance of their remains, more numerous than any animals of those times. They were gregarious. and must have roamed over Eastern Nebraska in countless millions. In size they ranged from an animal not larger than a raccoon to one as large as a small elk. The number of species of this family clearly defined is not less than twenty-five. The herbivora, however, did not hold undisputed possession of the land. The happiness of these countless herds was interrupted by most sanguinary enemies. The carnivorous mammalia were present in numbers proportionate to the herbivorous animals. Among the most bloodthirsty were the hyaenodontidae. "The genus hyaenodon combined the characters of the wolf, tiger, hyena, weasel, raccoon and opossum."--(Leidy) It was therefore one of the most comprehensive types of carnivorous mammalian animals that ever existed. The largest of the species was H. horridus, and was about the size of the largest of the black bears. The dentition of this animal was the most formidable conceivable. "In addition to powerful canine teeth, three of its molars were structured after the single sectorial tooth of other carnivorous mammals, though the last alone reached the full development of the corresponding tooth of the latter. The last of the series of molars were formed like those of the lion and tiger. These teeth--the strongest and broadest--combined the mechanism of the wedge and scissors, and were eminently adapted for cutting tissues and bones. Immense temporal fossae occupied the sides of the skull for the attachment of the powerful muscles that operated the levers that moved the lower jaw. The skull was about a foot in length. No animal living cotemporaneously with this formidable creature could have resisted its power."--(Leidy.)
Several other but smaller species of the same genus were cotemporary with it. The cat family were also here at the same time. Among the most remarkable of the family was a genus of saber-toothed lions (drepanodon). Its remains were first found in Western Europe, afterward in Greece and Asia, and finally in both Americas. The largest species equaled the lion and tiger in size, and, judging from their terrible array of destructive teeth, were even of greater ferocity.
Several species of monkey chattered in the forests of Nebraska during this same epoch. These animal forms are only a small portion of the species that have been found, and those found are evidently only a small part of those that existed here during Miocene times. Therewas here during this long epoch a most happy combination of forests, savannas and climate. Warm, temperate conditions existed almost to the Poles. Countless numbers of the mammalia here enjoyed a happy existence. These conditions were most favorable for that evolution of species that had produced the more highly specialized forms with which the epoch had commenced, and which was destined to be more perfectly developed during the next epoch.
Toward the close of the Miocene, the plateau legion was in process of further elevation; the lakes were drained or shifted eastward, and the region of the plains was still more depressed. This sinking of the plains extended far to the south, almost to the gulf, and to the east in its central portion about to where Columbus is located, on the Union Pacific Railroad, and for an unknown distance to the north. On the Niobrara, its eastern line was near the mouth of the Keya Paha, or Turtle Hill River. On the Republican, it was near the center of Harlan County. It thus changed the whole aspect of the western half of the continent. Coincident with this movement, great fissures were formed in the Cascade Range, and great floods of lava poured out, which, in North California, covered in wide sheets a great extent of country several hundred feet thick. The lava flood in Oregon in places was 3,000 feet thick, and covered at least 80,000 square miles. This great lava flood could not have come, as Richthofen has shown, from craters, but from earth fractures and fissures.
To the life then on the globe it must have been an event so appalling that the overthrow of Pompeii and Herculaneum, and the great Lisbon earthquake, in comparison with it, would have been an insignificant event. The throes of this event must have shaken the globe and affected all life, vegetable and animal. And as a matter of fact, the entire facies of the animal life of the globe was changed from this time forward, so we shall presently see. Thus was closed the Miocene epoch.