BY PROF. SAMUEL AUGHEY, PH. D., LL. D., PROFESSOR OF NATURAL SCIENCES IN THE UNIVERSITY OF NEBRASKA.
Produced by Gary Martens and Laurie Saikin
GEOLOGY is the poetry and romance of science. That alone would make its study obligatory on every cultivated intellect. But it is far more than that. It reveals the causes that make the material prosperity of a region possible. No one can fundamentally understand his section or State unless he knows its geology.
As now understood from its rock memorials, there have been five great eras in geological history, viz., the Archaean, Paleozoic, Mesozoic, Cenozoic, and Pscychozoic. During the early part of the first or Archaean era, our globe was companion star to the sun, and glowed by a heat and shone by a light of its own. The basaltic rocks are believed best to represent the physical characters of the earth's crust at the beginning of recorded geological history. From such materials, when our globe came to be sufficiently cooled down, were formed, by the asserting power of water, the sediments that were subsequently metamorphosed into the gneissic, granitic and other rock masses that constitute the Laurentian and Huronian strata of the earth's crust. As the rocks of these epochs still left in Canada are 40,000 feet thick, and at least as extensive in the Rocky Mountains and the Sierras, and still greater in Bohemia and Bavaria, after being subjected to numberless ages of erosion, the time represented by their deposition was greater, probably, than the whole of geological history since their close. So far as we now know, during all this immensely long era, there was no dry land in Nebraska. Then followed what geologists call
because of the antique or old life form of all animals and plants that appeared. The earlier portions are known as the Silurian ages, during which invertebrate life was dominant, and especially moluscan life, and the continent was growing and extending southward from its Archaean nucleus. The next age, called often the age of fishes, and also known as the Devonian, followed, but neither in this nor the preceding age was there any dry land in Nebraska. Neither are there any known deposits of the next or Sub-carboniferous period, in this State. Even the millstone grit, so common in the East, under the coal, has not yet been found. We come now to
During the progress of this age, the first dry land appeared in Nebraska. It was one of the most wonderful ages in the history of the globe, for, during its progress, the thickest, most extensive and most valuable of all the coal beds were formed.
Where found in Nebraska.--The carboniferous deposits occupy the southeastern portion of the State. Proximately, the western boundary line commences at a point a little above Fort Calhoun, eighteen miles north of Omaha, and extends southwest, crossing the Platte near the mouth of Salt Creek; thence running southwest, a little east of Lincoln, and thence in the same direction crossing the State line near the middle of the Otoe Indian Reservation. All east of this line is mainly Upper Carboniferous.The Dakota group cretaceous sandstone, once covered this entire region, but was removed by erosion, and small patches of it are still found in isolated basins over this carboniferous area.
Character of the Carboniferous Rock.--The rocks of this age are here very varied in character. They are mainly made up of sandstones, conglomerates, shales, clays and variously colored limestones. The clays are frequently drab, ash-colored, ferruginous, indurated and, sometimes, greenish and brownish. The limestones are gray, blue, white and yellowish, and some of them quite silicious. Along the Platte, east of the mouth of Salt Creek, occur some of the finest possible beds of limestone suitable for building stones. Many of the limestone beds contain from 5 to 20 per cent of carbonate of magnesia. Moluscan, crinoidal and coral fossils abound in them. As the specific fossils here found are characteristic of the Upper Carboniferous rocks in Iowa, Missouri and Illinois, the Nebraska beds are placed in the same division. That this is their true position has been shown by several geologists on stratiographical grounds. The lower coal measures, when traced westward from Des Moines, are found to run under the Nebraska carboniferous rocks.
Coal.--Thus far only one valuable marketable bed of coal has been developed in our carboniferous measures. The one referred to is in the western part of Richardson County, in Town 1 north of Range 13 east, of the Sixth Principal Meridian, From the bank on Section 33, during the last two years, over 100,000 bushels of coal have been taken. A great deal has also been mined from the same bed, three-fourths of a mile southwest of the last. The coal is of fine quality, giving but little ash. The bed ranges from eighteen to thirty inches in thickness. The coal is in demand for local wants. No railroad gives them access to the markets of the State. It has not yet been determined how far this bed extends by any actual borings or shaftings. Other beds of coal exist over this region, at a geologically higher horizon, but nowhere have they yet been found of sufficient thickness to justify development. Coal of good quality is also mined to a considerable extent south and southeast of Pawnee City, where the beds range from twelve to eighteen inches in thickness. Whether they can be profitably worked yet remains to be determined. A bed of varying thickness was once opened on the Indian reservation in the southeastern part of Richardson County. Its thickness ranges from twelve to twenty-four inches. Many other localities have attracted attention, and at times raised hopes of a larger coal supply, though none of the beds were over eighteen inches thick, and the most of them were much less. The only exception to this is one at Aspinwall, where the coal reaches a thickness of from twenty to twenty-four inches. Truth compels the admission that the upper coal measures are comparatively barren of beds of coal that can be profitably worked. In Nebraska, the only profitable bed thus far opened in these measures are the ones in Richardson County. The State Geologists of Iowa, Kansas and Missouri found the upper coal measures of these States equally barren.
Coal in the Lower Carboniferous.--In 1865, Mr. Croxton, of Nebraska City, made near this place an artesian boring to the depth of 344 feet, without penetrating through the Upper Carboniferous. At 189 feet, a fifteen-inch bed of coal was struck, but none after that. The Union Pacific artesian well, at Omaha, struck the Lower Carboniferous, without, however, reaching the coal horizon. The artesian well at Lincoln, however, struck a thirty-inch bed, at a depth of 900 feet. At Ponca, coal was encountered four and a half feet thick, at a depth of 574 feet. All these borings indicate that while the upper coal measures are comparatively barren, the lower, as it does in Iowa, contains beds which might be, and at some time probably will be, worked. Along the Missouri, the geological equivalent of the lower productive coal-beds would be reached south of Omaha, at a depth ranging from 800 to 900 feet. As the whole of our coal territory has by no means been explored, it is yet possible to find other small workable beds similar to those in Richardson County.
Features of the Carboniferous Age in Nebraska.--All geologists admit that the Carboniferous age was a long one--an age whose length could not be measured by thousands, but by millions of years. During the greater part of this great age, Nebraska was occupied by an arm of the ocean. Sometimes for long periods this sea was turbulent, as is indicated by the rocks which so generally change their character within a few miles. Owing to this feature, the exact equivalent of the rocks at widely different stations is hard to distinguish, except along river bluffs where the strata are exposed for long distances. The limestones, having been formed in deep water, are more constant in character over wide areas. Many of the shales and conglomerates exhibit the character of off-shore deposits. The coal-beds are proof of a land surface near by, and of a boggy, swampy condition on the sites where they lie. As one foot of bituminous coal represents from nine to eleven feet of original peat, and many centuries are required for the formation of such an amount of vegetable matter, and, as these beds represent only an infinitesimal amount of the time during which the events of this acre were in progress, it is additional proof that its length was beyond all calculation. During its progress, deep seas and shallow seas, quiet seas and turbulent seas, and vast swamps and bogs near to slightly elevated land masses, in turn predominated.
Vegetation.--The vegetation of the Carboniferous age was remarkable for its wide distribution, its luxuriance, its antique form, its complexity and its extreme beauty. The conifers that then existed, and which were the most advanced in type of all the vegetable forms, flourished mainly on the uplands. The most of them were of Araucarian type, which still flourishes in low latitudes, and mainly south of the equator. The fern family culminated in that age, many species growing to the dimensions of trees, and with a gracefulness and beauty unsurpassed by any vegetable forms of the present day. Many hundreds of species flourished over and around the forming coal-fields of the West. Calamites, allied to our scouring rushes, of tree size, were also abundant. Two great orders, more abundant in the number of individuals than any others, the Lepidodendrids, and Sigillaria, are no longer in existence. The Lepidodendrids had a dense bark, underneath which was a dense mass of loose tissue, through the center of which ran a small cylinder with a distinct pith. Such a structure adapted it most admirably, when flattened down, for flakes of coal. The Sigillarias, with "trunks fluted like Corinthian columns," and ornamented with seal-like impressions in verticle ranks, and "with a few large branches and long needle-like tapering leaves," were unfitted for anything except to minister to the beautiful and make coal. It is remarkable that, in that distant past, the jungles and forests of the globe were as remarkable for beautiful forms as the woodlands of to-day.
Animal Life.--Animal life during this age was abundant, though, as in the vegetable kingdom, the forms were mostly antiquated. One of the most abundant of all in individuals was a curious little animal, already referred to, and which is frequently called fossil wheat or rice. It is, however, a real but lowly animal, classed with the protozoans, and known as Fusilina cylindrica. It is nearly the shape and about the size of a grain of wheat. Its shell is composed of seven or eight closely-coiled whorls. Unlike its condition in Europe, it here ranges all through the coal measures. It is questionable whether it is anywhere in America so abundant as it is here in Nebraska. In many places around Tecumseh, it constitutes almost theentire fabric of many rocks, often from four to ten feet in thickness. Enormous numbers occur in shale, and, in fact, almost every kind of our carboniferous rocks. Even the massive compact limestone from Staut's quarry, at South Bend, contains them in immense numbers, which gives the rock great beauty when polished.
Corals, which are now confined to low latitudes, were very abundant in Nebraska during carboniferous times. The most characteristic is known as ramshorn coral, or Campophyllum torquium.
The screw-like stems of crinoids are observed in all our carboniferous rocks.
Moluscan life flourished in an extraordinary degree. Not less than ninety-five species have been identified here from these deposits.
Of the five species of crustaceans found fossil in these rocks, three are trilobites of the genus Phillipsia.
Vertebrate life was represented principally by fishes, of which eight species have been described by St. John. Many more have been found, which are not yet identified.
Climate.--The vegetable and animal life of the Carboniferous age indicate that its climate was not subject to extremes, at least not during the epochs when the rocks were deposited, whatever it may have been during the transition intervals. It was neither intensely hot nor cold. It was just such a climate as a constantly cloudy murky atmosphere, over semi-continental levels and flats, would naturally produce.
Close of the Carboniferous Age.--In the eastern portion of the continent, the Carboniferous age was evidently closed by the Appalachian revolution. This great uplift was evidently continental in character, the level of the land on each side being raised along with it. This was no sudden convulsion. The Appalachians commenced to rise long before the close of the age, and during its progress a point was reached when the old conditions were passed and new ones inaugurated. Vegetable and animal life partook of the change and the whole movement inaugurated or constituted
This age was the last volume in the history of Paleozoic life. The great Appalachian revolution was only partially completed, for the upward movement still continued. The peculiarities of the coal age had ceased, but its impress was left on Permian times. While the upward movement was advancing toward completion at many places, especially in Europe and Asia, around the borders of the old coal-fields, depressions still existed for extensive seas which received the sediments that entombed and preserved the organic remains of the age.
Hence, we have records of the earlier part of the age, but none of its latter portion, because the continents reached such an elevation that all the seas were drained, and no place was left to stow away the debris and worn-out life of the period. The process of uplifting, therefore, was continued until the continent was raised above even its present level, during which none of its monuments could be preserved. The whole latter portion, therefore, of the Permian, a portion of time incalculably long, is a lost interval in geological history. The conditions now became favorable for the complete drainage of the continent. Lofty mountains and steep inclinations toward plains produced great rivers. Clear skies took the place of murky ones in the previous age. The seasons had gradually become more changeable and varied. The old vegetable and animal life was not adapted to these conditions, and hence it, too, had to change or perish. During this lost interval occurred those mighty changes in the fauna and flora of the globe, which transformed Paleozoic life into the Mesozoic forms which appeared in the next age.
In Nebraska, the western boundary of the Permian passes a little west of south a few miles east of Lincoln, extending to Beatrice and thence into Kansas. Opposite Lincoln, it is only a few miles wide, but broadens going southwest and through Kansas. Toward its western side, it passes under the Dakota group of the cretaceous. It is however, as already intimated, only the lower Permian that is here represented. Before the middle Permian was reached, this entire region was drained and had become a dry land surface, and hence no memorials of its history were preserved.
Character of the Permian Rock.--Near Beatrice there are many exposures of yellowish and bluish magnesian limestone, full of geode cavities, lined with calc-spar. This rock occurs in layers from four inches to two feet thick, and the whole series of strata are from twelve to twenty feet thick. Below this there is a bed of yellow compact limestone, from eighteen inches to three feet thick. Next below, there is a thickness of from eight to twelve feet of a dark grayish clayey limestone, also full of geode cavities, lined with crystals of calc-spar, and sometimes of silicate of lime or pure silica. This stratum often becomes light colored on exposure to the air, and occasionally it becomes massive cream-colored limestone. Wherever, therefore, such beds as thus described are found in Nebraska, bordering the upper carboniferous rocks, they invariably indicate our Permian deposits. Toward the east, in Pawnee County, they run out, as the carboniferous then becomes the surface rock, which, on the contrary, in a westward direction, runs under the Permian. Above the first of these Permian rocks there is a bed of variegated clay, and sometimes of potter's clay, whose geological age is uncertain, but which probably belongs to the Dakota group of Cretaceous rocks, which comes in next above. This Dakota group is recognized by its dark gray, brownish and red sandstones, which around and westward from Beatrice overlies the Permian.
There are no known deposits of the earlier portions of the Mesozoic--the Triassic and Jurassic--in Nebraska. The deposits, however, of the last portion of the Mesozoic era, the cretaceous, rest directly on the Permian, and where the latter is absent on the carboniferous. Two explanations of this are possible. Either the Triassic and Jurassic were removed by erosion before the cretaceous was laid down, or, which is more probable, this region was a land mass during early Mesozoic times. We have already seen that the Carboniferous age was brought to a close by an upward movement of the continent, and that this movement continued through the Permian, until much of the previous water surface was drained, and made it impossible to preserve the memorials of its latter history. The same events that prevented the preservation of the memorials of the Permian would, if continued, prevent the deposition of Triassic and Jurassic rocks. With a large degree, therefore, of certainty, we may rest assured that during these periods Nebraska was an extended land surface, and if so, there must have flourished here for countless centuries the peculiar vegetable and animal life of those times.
Length of the Trio-Juro Periods.--The length of the Trio-Juro periods can be ascertained only relatively. Not even an approximate estimate can be made, but all geologists admit that they were long periods. This opinion is based on the fact that in the Rocky Mountain region the sediments reach 3,800 feet in thickness, a large portion of which are of that character that never accumulate rapidly. The time involved in the accumulation of sediments in sea bottoms has been variously estimated from one inch to one foot a century, at the latter rate, the time involved would be 315,000 years. During all these lone centuries, therefore, and long into the cretaceous, Nebraska existed as an extensive land surface. The imagination alone can, with the few data from the vegetable and animal life of the time, fill out but very imperfectly this lost page in our geological history.
Vegetable Life.--Nebraska, during these periods, owing to its position, andbecause bounded on the west and south; west by seas of great extent, had a warm, temperate and moist climate. The peculiar forms of the Mediaeval world greatly flourished here at that time. Among these in the Triassic period were huge tree ferns, cycads and conifers, these last being araucarians, a family now confined mainly to South America and Australia. In the succeeding Jurassic, the vegetation was similar and the conditions on the whole still more favorable for gigantic growths. To this period belong some of the coal-fields of Scotland, England, India, China, Eastern Virginia and North Carolina. It is probable that, while the conditions under which coal was formed were similar in all geological times, the plants differed exceedingly. The higher cryptogams obtained in carboniferous times, but in the Triassic ferns, and especially conifers and cycads were the common forms. The Jurassic was eminently the age of naked seeded trees (gymnosperms), especially the cycads, which at that time culminated in the number of species and individuals. Even three-fourths of all the fossil zamiae, and one-half of the cycads known from all the geological formations, are from the Jurassic. No one can look at a cycad, with its long, fernlike leaves, without, admiring its beauty. These vegetable forms are now confined to low, moist latitudes, but for immense periods of geological time, they were the dominant type on what are now the plains of Nebraska. Here, in those times, long with tree ferns and araucarians, they made immense thickets and forests.
Animal Life.--The Mesozoic was eminently what is so often called a Reptilian age. All kinds of vertebrate life took on more or less of this type. Nebraska being then a land surface, we will pass over the life of the seas. The Atlantosaurus beds of Marsh in the Jurassic of Colorado indicates the land fauna of the period. Nebraska then drained westward, and its land animals at flood-time were carried in that direction from the river bottoms where they had perished. Among these was probably that largest land animal yet found in rocks of any age-the Atlantosaurus immanis (monstrous sized lizard). It had a femur eight feet four inches long, which would indicate an animal, when standing on all fours, of over thirty feet in height and one hundred feet in length. Other forms of gigantic mold also existed here at the same time. Among these largest of all Dinosaurs, some of the smallest yet found also existed. One of the earliest mammals, structured like an opossum, some reptilian birds and a crocodile; with the fish-like character of biconcave vertebra, also appeared among these reptilian forms. For untold ages, these curious animal forms flourished amid the colossal forests of our Nebraska plains.
Close of the Trio-Jurassic Period.--The Trio-Jurassic period was brought to a close by a further contraction of the cooling globe. One of the results of this contraction was, according to Whitney, the uprising of the Sierras. The rocks of the next period (Cretaceous) lie unconformably on or against its side. At the same time, the Wasatch, almost parallel with the Sierras, and the Uintas, almost at right angles with the last, also came up from the bottom of the old Jurassic sea. This probably raised the whole of this portion of the continent to so high a level as to drain the whole of what had been the Jurassic Sea, and constituted it a land surface until the middle Cretaceous period.