Produced by Gary Martens and Laurie Saikin
The Loess deposits first received this name in America from Lyell, who observed them along the Mississippi in various places. The name was used previously in Europe to designate such materials in the valley of the Rhine and the Danube. Heyden called them the bluff deposits, because of the peculiar configuration they give to the uplands that border the flood plains of the rivers. This deposit, though not particularly rich in organic remains, is in some respects One of the most remarkable in the world. Its value for agricultural purposes is not exceeded anywhere. It prevails over at least three-fourths of the surface of Nebraska. It ranges in thickness from 5 to 150 feet. Some sections in Dakota and other counties measure over 200 feet. Even at North Platte, 300 miles west of the Missouri, on the south side of the river, the thickness varies from 125 to 150 feet.
From Crete, on the Burlington & Missouri River Railroad, west to Kearney, on the Union Pacific Railroad, its thickness for ninety miles ranges from forty to ninety feet. Along the Republican, the formation, of various thickness, extends almost to the west line of the State. It is generally almost homogeneous throughout, and of almost uniform color, however thick the deposit or far apart the specimens have been taken. I have compared many specimens taken 300 miles apart and from the top and bottom of the deposits, and no difference could be detected by the eye or by chemical analysis.
Physical Character of the Loess.--Over 80 per cent of this deposit is very finely comminuted silica. When washed in water, left standing, and the water poured off, and the coarser materials have settled, the residuum, after evaporation to dryness, is almost entirely composed of fine silicious powder. So fine, indeed, are the particles of silica, that its true character can alone be detected by analysis or under the microscope. About 10 per cent is composed of the carbonates and phosphates of lime. These materials are so abundant in these deposits, that they spontaneously crystallize, or form concretions, from the size of a shot to that of a walnut; and these are often hollow or contain some organic matter, or a fossil, around which the crystallization took place. Almost anywhere, when the soil is turned over by the plow or in excavations, these concretions may be found Often, after the rain has washed newly thrown-up soil, the ground seems to be literally covered with them. Old gopher hills and weather-beaten hillsides furnish these concretions in unlimited quantities for the geologist and curiosity hunter. When first exposed, most of these concretions are soft enough to be rubbed fine between the fingers, but they gradually harden by exposure to the atmosphere. This deposit also contains small amounts of alkaline matter, iron and alumina. For the purpose of showing the homogeneous character and the chemical properties of the Loess deposits, I have made many analyses of these peculiar deposits, five of which are here given as samples. No. 1 is from Douglas County, near Omaha; No. 2, from the bluffs near Kearney; No. 3, from the Lower Loup; No. 4, from Sutton, and No. 5 from the Republican Valley, near Orleans, in Harlan County:
================================================================ | No.1. | No.2. | No.3. | No.4. | No.5. _________________________|_______|_______|_______|_______|______ Insoluble (silicious) | | | | | matter..............| 81.28 | 81.32 | 81.35 | 81.30 | 81.32 Ferric oxide.............| 3.86 | 3.87 | 3.87 | 3.85 | 3.86 Alumina..................| 75 | .75 | .74 | .73 | .74 Lime (carbonate).........| 6.06 | 6.06 | 6.03 | 6.05 | 6.09 Lime (phosphste).........| 3.59 | 3.59 | 3.58 | 3.57 | 3.59 Magnesia (carbonate).....| 1.28 | 1.28 | 1.31 | 1.31 | 1.29 Potassa..................| .27 | .29 | .35 | .34 | .33 Soda.....................| .15 | .16 | .14 | .16 | .16 Organic matter...........| 1.07 | 1.06 | 1.05 | 1.06 | 1.06 Moisture.................| .1.09 | 1.08 | 1.09 | 1.08 | 1.09 Loss in analysis.........| .59 | .54 | .53 | .55 | .47 |_______|_______|_______|_______|______ |100.00 |100.00 |100.00 |100.00 |100.00 _________________________|_______|_______|_______|_______|______
|For the purpose of comparison, I here reproduce. from Hayden's report, Bischoft's analyses of the Loess of the Rhine:|
================================================================ | NO. OF ANALYSIS. |_______________________________________ | 1. | 2. | 3. | 4. | 5. ________________________|_______|_______|_______|_______|_______ Silicic acid............| 58.97 | 79.53 | 78.61 | 62.43 | 81.04 Alumina.................| 9.97 | 13.45}| | 7.51 | .75 | | }| 15.26 | | Peroxide of iron........| 4.25 | 4.81}| | 5.14 | .67 Lime....................| 0.02 | 0.02 | ..... | ..... | ..... Magnesia................| 0.04 | .06 | 0.09 | 0.21 | 0.27 Potash .................| 0.11 | 1.05}| | | | | }| 3.31 | 1.75 | 2.27 Soda....................| 0.84 | 1.14}| | | Carbonate of lime.......| 20.16 | ..... | ..... | 11.63 | ..... Carbonate of magnesia...| 4.21 | ..... | ..... | 3.02 | ..... Loss by ignition........| 1.37 | ..... | 1.89 | 2.31 | ..... ________________________|_______|_______|_______|_______|_______
It will be seen from the above analyses of Bischoff that Nos. 3 and 5, in the quantity of silica and other elements that are present, come very near the Loess of Nebraska. The principal difference is the larger quantity of alumina present in the samples analyzed by Bischoff. Chemically, the deposits of the Rhine Valley, as Hayden remarks, are not essentially different from those of the Loess soils along the Missouri.
Fertility and Agricultural Value of the Loess.--As would be expected, from the elements which chemical analysis shows to be present in these deposits, it forms one of the best soils in the world. In fact, it can never be exhausted until every hill and valley of which it is composed is entirely worn away. Its drainage, which is the best possible, is owing to the remarkably finely comminuted silica of which the bulk of the deposit consists. Where the ground is cultivated, the most copious rains percolate through the soil, which, in its lowest depths, retains it like a huge sponge. Even the unbroken prairie absorbs much of the heavy rains that fall. When droughts come, the moisture comes up from below by capillary attraction And when it is considered that the depth to the solid rock ranges generally from 5 to 200 feet, it is seen how readily the needs of vegetation are supplied in the driest seasons. This is the main reason why over all the region where these deposits prevail. the natural vegetation and the well-cultivated crops are rarely dried out or drowned out. I have frequently observed a few showers to fall in April, and then little more rain until June, when there is generally a rainy season of from three to eight weeks' continuance. After these June rains, little more would fall till autumn; and yet if there was a deep and thorough cultivation. the crops of corn, cereals and grass would be most abundant. This condition represents the dry seasons. On the other hand, the extremely wet seasons only damage the crops over the low bottoms, subject to overflow. Owing to the silicious nature of the soils, they never bake when plowed in a wet condition, and a day after heavy rains the plow can again be successfully and safely used. In the interior, away from the Missouri, the surface of the Loess deposits is in places gently undulating and in places rolling. Not unfrequently a region will be reached, where, for a few miles, the country is hilly, and then gradually becomes, with all kinds of intermediate forms, almost entirely level. The bluffs that border the flood plains of the Missouri, the Lower Platte and some other streams are sometimes exceedingly precipitous, sometimes gently rounded off and sometimes in gentle slopes. They often assume fantastic forms, as if carved by some curious generations of the past. At present, they retain their forms so unchanged from year to year, affected neither by rain nor frost, that they must have been molded into their present outlines under circumstances of climate and level very different from those which now prevail.
Architecture on the Loess.--For all purposes of architecture, this soil, even for the most massive structures, is perfectly secure. A brick or stone building. if commenced below the winter frost line, never gives way. Even where the first layers of brick or stone are laid on top of the ground, there is seldom such unevenness of settling as to produce fractures in the walls. On no other deposits except the solid rock can there be such excellent roads. From twelve to twenty-four hours after the heaviest rains, the roads are perfectly dry, and often appear, after being traveled a few days, like a vast door formed from cement, and by the highest art of man. The drawback to this picture is that sometimes during a drought the air along the high ways on windy days is filled with dust. And yet the soil is very easily worked, yielding readily to the spade or plow. Excavation is remarkably easy, and no pick nor mattock is thought of for such purposes. It might be expected that such a soil readily yielded to atmospheric influences, but such is not the case. Wells in this deposit are frequently walled up only to a point above the water-line; and on the remainder the spade marks will be visible for years. Indeed, the traveler over Nebraska will often be surprised to see spade-marks and carved-out names and dates years after they were first made, where ordinary soils would soon have fallen sway into a gentle slope. This peculiarity of the soil has often been a God-send to poor emigrants. Such often cut out of the hillsides a shelter for themselves and their stock. Many a time when caught out on the roads in a storm, far away from the towns, have I found shelter in a "dug-out" with an emigrant family, where, cozy and warm, there was perfect comfort, with little expenditure of fuel on the coldest days.
Cause of the Physical Peculiarities of the Loess.--Carbonate of lime has entered into slight chemical combination with the finely comminuted silica. There is always more or less carbonic acid in the atmosphere which is brought down by the rains, and this dissolves the carbonate of lime, which then readily unites with silica, but only to a slight extent, and not enough to destroy its porosity. Though much of the silica is microscopically minute, and is water-worn or rounded, it still enters into this slight union with the carbonate of lime. Had there been more iron and lime in this deposit, and had it been subjected to a greater and longer pressure from superincumbent waters, instead of a slightly chemically compacted soil, it would have resulted in a yellow sandstone formation incapable of cultivation. There is not enough clay present to prevent the water from percolating through it as perfectly as through sand, though a great deal more slowly. This peculiarity causes ponds and stagnant water to be rare within the limits of this deposit. Where they do exist in slight depressions on the level plain, it is found that an exceptionally large quantity of clayey matter has been accumulated in the soil on the bottom.
Fruit of the Loess Deposits.--In these Loess deposits is found the explanation of the ease with which nature produces the wild fruits in Nebraska. So dense are the thickets of wild grapes and plums along some of the bottoms and bluffs of the larger streams that it is difficult to penetrate them. Over twenty varieties of wild plums have been observed. Two species of grapes have been distinguished. but these have interminable varieties. The same remark applies to the strawberries. Raspberries and blackberries abound in many parts of the State. The buffalo berry is common on many of the river bottoms of the State. Many other wild fruits abound and grow with amazing luxuriance wherever timber protects them and prairie fires are repressed. It is also a paradise for many cultivated fruits. They luxuriate in a soil like this, composed of such materials and with such perfect natural drainage. No other regions, except Loess regions elsewhere, can compare in those respects with Nebraska. The Loess of the Rhine supplies Europe with some of its finest grapes and wines. The success that has already attended the cultivation of the grape in Southeastern Nebraska at least demonstrates that this State may likewise become remarkable in this respect. For the cultivation of the apple its superiority is demonstrated. Though so young in years compared with other States, it has taken the chief premiums in the pomological fairs at Richmond and Boston. There are, of course, obstacles here as well as elsewhere. What is claimed is, that the soil as analysis and experience prove, is eminently adopted to the cultivation of the grape and the apple. The chief obstacle, especially in the interior, is climatic. In midsummer, occasional hot dry winds blow from the southwest, and the young apple trees need to have their trunks protected by a shingle until the top shades them. Any of the older orchardists can give the different methods by which this can be done.
Scenery of the Loess Deposits.--It has been remarked that "no sharp lines of demarkation separate the kinds of scenery that produce the emotions of the grand and the beautiful." This is eminently true of some of the scenery produced by the Loess formations. Occasionally, an elevation is encountered from whose summit there are such magnificent views of river, bottom, forest and winding bluffs as to produce all the emotions of the sublime. One such elevation is Pilgrim Hill, in Dakota County, on the farm of Hon. J. Warner. From this hill, the Missouri bottom, with its marvelous, wierd-like river, can be seen for twenty miles. Dakota City and Sioux City, the latter distant sixteen miles, are plainly visible. If it happens to be Indian summer, the tints of the woods vie with the hazy splendor of the sky to give to the far outstretched landscape more than an Oriental splendor. I have looked with amazement at some of the wonderful cañons of the Rocky Mountains, but nothing there more completely filled me and satisfied the craving for the grand in nature than did this view from Pilgrim Hill. There are many landscapes everywhere of wonderful beauty along all the principal rivers. The bluffs are sometimes precipitous, but generally they round off and melt into gently rolling plains. They constantly vary, and in following them you come now into a beautiful cove, now to a curious headland, then to terraces, and however far you travel you can look in vain for a picture like the one just passed.
True Origin of the Loess Deposits.--Geological events have already been traced to the beginning of the Loess period. According to Newberry, the whole of the old forest bed area, now less than 1,100 feet above the level of Lake Erie, was flooded by the changes of level and thawing of retreating glaciers that followed its disappearance. In Nebraska during this time, icebergs again floated over the waters. The farther retreat of the glaciers and the elevation of Eastern Iowa reduced the area of this great lake. What had been a great interior sea of turbulent waters had now become a system of placid lakes that extended from Nebraska and Western Iowa at intervals to the Gulf. The Missouri drained through them all along its length. The Missouri, and sometimes the Platte, have been amongst the muddiest streams in the world. If we go up the Missouri to its source, and carefully examine the character of the deposits through which it passes, we cannot be surprised at its character. These deposits. being of Tertiary and Cretaceons ages, are exceedingly friable and easy of disintegration. The Tertiary and especially the Pliocene Tertiary, is largely silicious, and the Cretaceous is both silicious and calcareous. In fact, in many places the Missouri and its tributaries flow directly over and through the chalk-beds of the cretaceons deposits. From these beds the Loess deposits no doubt received their per cent of the phosphates and carbonates of lime. Flowing through such deposits for more than a thousand miles, the Missouri and its tributaries have been gathering for vast ages that peculiar mud which filled up their ancient lakes, and which distinguishes them even yet from most other streams. Being anciently, as now, very rapid streams. as soon as they emptied themselves into these great lakes and their waters became quiet, the sediment held suspended was dropped to the bottom. While this process was going on in the earlier portion of this age, the last of the glaciers had not retreated further than a little beyond the northern boundary of the Loess lake, and then gradually to the head-waters of the Platte, the Missouri and the Yellowstone. Aided by the erosive action of ice, these mighty rivers must have been vastly more rapid and energetic at that time than in their recent history. The following analysis of Missouri River sediment taken at high stage will show, by comparison with the analyses of Loess deposits, what a remarkable resemblance there is even yet between the two substances. In one hundred parts of Missouri River sediment there are of--
Insoluble (silicious) matter...................... 82.01 Ferric oxide...................................... 3.10 Alumina........................................... 1.70 Lime, carbonate................................... 6.50 Lime, phosphate................................... 3.00 Magnesia, carbonate............................... 1.10 Potassa........................................... .50 Soda.............................................. .22 Organic matter.................................... 1.20 Loss in analysis.................................. .07 ------- 100.00
This comparative identity of chemical combination points to the remarkable sameness of geological conditions that have existed for long periods in the Upper Missouri and Yellowstone regions.
After these great lakes were filled up with sediments (Missouri mud), they existed for a longer or shorter time? as already remarked, as marshes and bogs. Isolated portions would first become dry land. As soon as they appeared above water, they became covered with vegetation, which, decaying from year to year, and uniting under water, or at the water's edge, with the deposits at the bottom, formed the black soil so characteristic of Nebraska prairies. For it is well known that when vegetable matter decays in water or a wet situation, its carbon is retained. In dry situations, it passes into the atmosphere, as carbonate acid gas. After the first low islands appeared, they gradually increased in size and numbers until dry land conditions prevailed. The ponds and sloughs, some of which are almost lakes, still in existence, are probably the last remains of these great lakes. The rising of the land continuing, the rivers began to cut new channels through the middle of the old lake beds. This drained the marshes and formed the bottom lands as the river of that period covered the whole of the present flood plains from bluff to bluff. It was then when the bluffs were new and more plastic that they were first sculptured by rains, frosts and floods into their present unique forms. The Missouri, during the closing centuries of the Loess epoch, must have been from five to thirty miles in breadth, forming a stream, which, for size and majesty, rivaled the Amazon.
The Platte, Niobrara and Republican covered their respective flood plains in the same way. In the smaller streams of the State, those that originated within or near the Loess deposits, such as the Elkhorn, Loup, Bow, Blue and the Nemahas, we see the same general form of flood plain as on the larger rivers, and no doubt their bottoms were also covered with water during this period. Hayden, in his first reports, has already expressed the same opinion as to the original size of these rivers. Only a few geologists will dissent from this view. The gradually melting glaciers, which had been accumulating for so many ages at the sources of these great rivers, the vast floods of water covered by the necessarily moist climate and heavy rains, the present forms and materials of river bottoms, are some of the causes which, in my opinion, would operate to produce such vast volumes of water. The changes of level were not all upward during this period. The terraces along the Missouri, Platte and Republican indicate that there wore long periods when this portion of the continent was stationary. Several times the movement was downward. Along the bluffs in the Republican Valley, at a depth varying from ten to thirty feet from the top, there is a line or streak of the Loess mingled with organic matter. It is, in fact, an old bad, where vegetation must have flourished for a long period. It can he traced from Orleans upward in places for seventy-five miles. It indicates that after this bed had, as dry land, sustained a growth of vegetation, an oscillation of level depressed it sufficiently to receive a great accumulation of Loess materials on top of it. Other oscillations of this character occurred previously to and subsequent to this main halt. These have already been discussed. I have also found traces of this movement in many other portions of the State.
Length of the Loess Epoch.--Comparing the present deposits of the Missouri with those of Loess times, an approximate estimate may be made of the length of that epoch. The great lakes of the Loess epoch extended with few interruptions almost to the Gulf, and some of them covered an area of 45,000 square miles. Were all the sediments which are at present brought down the Missouri spread over such a vast area, the annual thickness of the deposit would be less than one-sixteenth of an inch. Probably the yearly accumulation of the sediment during the Loess epoch amounted to that much, owing to the then greater volume of the Missouri and the aids to erosion from the greater prevalence of ice near its sources. The highest bluffs represent the original level of the Loess deposits before the tremendous erosive agencies which removed so much of their materials had done their work. Now, in places, these sediments are even yet 200 or more feet in thickness, so that it would be safe to estimate the average thickness of the original deposits at 100 feet. A yearly increase of one-sixteenth of an inch in thickness would at this rate have required 19,200 years to form these deposits. This is a very low estimate for the length of the Loess epoch.
Life of the Loess Epoch.--Both land and fresh-water shells are abundant in the Loess of Nebraska. The former were no doubt brought into the Loess lake at flood time. The shells are largely such as are still to be found in the same region. Teeth and the stray bones of fishes are sometimes met with. The remains of rabbits, gophers, otters, beavers, squirrels, doer, elk and buffalo are frequently found. Through the entire extent of these deposits the remains of these mastodons and elephants are abundant. In 1870, I found an arrow head in the Loess in a railroad cut three miles east of Sioux City, Iowa. It was in undisturbed Loess. My next find of human relics occurred two and a half miles southeast of Omaha, in a railroad cut, where a large arrow or spear head came to light twenty feet below the top of the Loess. Thirteen inches above this arrow head was the lumbar vertebra of an elephant. Subsequently, additional arrow heads were found in the Loess of the Republican Valley. Primitive man was therefore cotemporary of the elephant around the shores of this old lake in Loess times.
Close of the Loess Epoch.--The upward movement that had begun at the close of the second subsidence epoch of the Quaternary finally brought the Loess age to a close. As the land rose most toward the west and north, the area of this Loess lake was gradually lessened from these directions, and its remnants were last active on its southeastern border. This explains the fact already mentioned in other connections, that the long, gentle slopes of the bluffs bordering the hood plains running in an easterly and westerly direction are almost universally on the north side of the valleys. The closing of the Loess period first clearly outlined the present rivers of Nebraska, when they covered the whole of the bottoms, from bluff to bluff, and when the mud flats of the former Loess lake themselves constituted the flood plain. So far as known, no convulsive movements to a certainty accompanied the close of this period. Many movements of this kind occurred in the regions of the mountains during the Quaternary, but they have not yet been synchronized with geological events on the plains.
Terrace Epoch.--From the preceding, it is evident that the Terrace epoch in Nebraska is closely connected with that order of events and with those changes that finally resulted in the present order of things in Nebraska. It commenced here after the close of the Loess period. When the rivers covered the whole of the existing bottoms, and had the rid Loess lake bed for a flood plain, the land still lay far below its present level, and was in the transition stage between the Loess and Terrace periods. When the elevation became a little greater, and the drainage better, and the volume of water less, it cut a new channel amid its old bed, which now constituted its flood plain. This formed the first terrace, and fully inaugurated this epoch. Here, the land and the river must have stood for ages. Again there was an upward movement, the drainage became still better, the volume of water lessened and another channel formed, and the previous river bed changed to a flood plain. Thus terrace after terrace was formed, each representing a stage of quiet in the upward movement of the land. There are indications that this upward movement continued until this section stood considerably above its present level. Subsequently, a period of subsidence occurred, during which the river channels were silted up. This process of silting up continued to recent times. At present, the indications are that there is a slight upward movement of the continent, amounting to perhaps one or two feet to the century.
The terraces made during this epoch occupy various heights above the flood plains. The one next to the rivers in the interior ranges from three to six feet above the lowest bottom. The next is from twelve to twenty-five feet above the first, and a third at varying heights above the last. Often terraces intermediate between these are detected. They vary so much in height that the system ascertained to exist at one place is no guide for the next river. This variation, no doubt, is partly caused by one or two or more corresponding terraces being removed by subsequent erosion. They are the memorials of the rivers' former stay for an indefinite time at that level. It is possible that this Terrace epoch was as long as the Loess period, but of this there is no certainty, as it partakes in part of the character of a lost interval of geological history.