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other material and lodged here and there wherever the current velocities permitted.

The clays and silts vary in character from place to place and at different depths. Occasionally almost pure masses of clay are found, beds almost entirely free from admixtures of sand, clay with a high degree of plasticity and in every respect resembling the purest known, except that it contains sufficient impurities to modify its color. Frequently such masses of clay seem to be colored with decaying organic matter, as though during its accumulation such matter in one form or another was present, at least in limited quantities. Elsewhere the color of the clay seems to indicate the absence of organic matter of any kind.

The stratigraphic property of the clay is interesting. In places it exists in broad layers, apparently extending for miles in unbroken beds. Elsewhere it forms lenticular masses, oblong in horizontal dimensions and irregular in peripheral outlines. Sometimes it is interbedded with the heavy gravel and sand beds, and elsewhere seems to be relatively distinct from them.

Along the Arkansas River Valley, near the bluffs north of Garden City, a heavy bed of clay nearly 100 feet thick extends up and down. the valley for 4 or 5 miles. Its north-south diameter is usually about half a mile. South of the river 12 or 15 miles from Garden City is another locality in which occur irregularly shaped clay beds or clay bowlders, as they are locally called. During August, 1896, a well was drilled about three-fourths of a mile south of Atwater, in Meade County. It went to the surprising depth of 288 feet, passing through nothing but a light-blue plastic clay almost the entire depth. Other wells on every side of this one, from 1 to 2 miles away, found the usual amount of water-bearing sand at from 20 to 40 feet. Such illustrations could be multiplied until the whole of the Tertiary of Kansas was covered. Everywhere such irregularities exist. Few wells have been made which did not pass through both sand and clay. Even in the sand hills south of the Arkansas River the few wells dug or bored invariably found clay. The State well in the sand hills just south of Cimarron may be taken as an example. At a depth of 23 feet a bed of remarkably compact plastic clay was reached, about 5 feet in thickness.

In many places in western Kansas and elsewhere on the plains a small amount of a fine-grained matter is found, which is generally, called volcanic ash. A few deposits of the same material have been found in this territory. The best exposure known is along a tributary to Crooked Creek, about three-fourths of a mile west of Meade Center, although other lesser deposits are known in Meade County and elsewhere.

Over a large portion of the whole Tertiary area of the plains the surface is covered with a fine-grained soil which has so high a percentage IRR 6-3

of clay within it that it has a relative high plasticity and other properties that have given it the name "Plains marl." It covers more than half of the surface, but by no means all of it. Neither is it confined to the surface, for often the same kind of material is found interbedded between layers of other materials. It is probably composed of the finest silt and clay particles which migrated eastward during Tertiary time and were lodged here and there wherever the conditions of water velocity dictated. In recent times, also, the winds have exerted a sorting action on the surface materials, which has helped to make the Plains marl more characteristic. The strong winds pick up the finest dust and carry it for miles and deposit it wherever a suitable lodging can be secured. This not only concentrates the finest materials together by movement, but also leaves the coarser soils and sands behind, so that the same process produces sand dunes and sandy soils which are often mere residual products after the finer silt has been blown away.

The structural relations of the different Tertiary materials are far from regular. It is doubtful if there can be any definite stratigraphic relations established covering a considerable scope of country. The gravel and sand are frequently cemented into a moderately firm rock by the presence of a variable amount of a calcium carbonate cement. This cement is sometimes found in the clay as well, but it is most abundant in the sand and gravel, producing a sort of sandstone or conglomerate to which the name "mortar beds" or "grit" is generally applied. Some of the varieties of this are the so-called "natural mortar," which is extensively used throughout the West for making a mortar to plaster with and to roof houses. These mortar-bed horizons are prominent features in many places and constitute the only hard and resisting strata in the Tertiary. The idea so frequently expressed, that they are located near the base of the Tertiary, is correct for some localities, but incorrect for others.

Along the Buckner, in the southwestern part of Hodgeman County, the sand and gravel are as firmly cemented as at any place known to the writer. Here they form a tolerably solid rock which lies at the top of the bluffs on the south side of the Buckner. They are in beds from 10 to 20 feet thick, varying much more than ordinary sandstone beds do. Below them in this locality the bluffs are composed of a looser and finer material. At other places along the Sawlog, near by, the mortar beds are found near the bottom of the Tertiary, and not infrequently resting immediately upon the Benton limestone.

The north bluff line of the Arkansas River from some distance below Dodge westward almost to Garden is protected by a well-developed mass of mortar beds. Throughout the most of this distance three distinct layers of mortar beds can be traced, while in other places four or more may be found. They are composed of cemented sand and coarse gravel, and are separated from each other by beds of clay and fine sand. The weathering processes wear away the soft

clay beds more rapidly than the mortar beds, producing a series of narrow terraces along the bluffs similar to those generally observed in places where the limestones and shales alternate with each other, as so frequently occurs in the eastern part of the State.

South of the Arkansas River but little of the mortar-bed material is to be seen until the vicinity of Crooked Creek and the Cimarron is reached. Here we have the same lack of regularity so noticeable elsewhere. The most pronounced form of the mortar beds is often found at the very summit of the bluffs, but by no means always so. In other places they occur midway up the bluff, and not infrequently near the base. The bluffs of Crooked Creek below Meade are good examples of this. On the eastern side of the creek they are very rugged, with frequent instances of mortar beds being well developed, but by no means do they form a constant stratum continuously along the bluff. On the western side the bluff line is not so abrupt, and consequently there is not so good an opportunity for observing the mortar-bed masses. To the southwest of Meade, along the upper portion of Spring Creek, however, some of the hilltops are very distinct, and the erosive forms are significant of hills with a protecting cap of hard material covering softer materials. These can well be studied from the Meade topographic sheet. A few of these hills are particularly noteworthy. On the north bluff of Spring Creek, about 4 miles above Crooked Creek Valley, the mortar beds are found lying at the summit of the hill. The sandy clay underneath is worn away, so that quite frequently the mortar-bed rock projects several feet, forming an overhanging cliff. South of Spring Creek a similar condition obtains. Hill point after hill point stands out in the landscape as a prominent feature, on the top of which a horizontal mass of mortar-bed rock serves as a protection to the soft and easily eroded sandy clays beneath.

Along the Cimarron River from some distance above Arkalon to where the river encounters the Red Beds near Englewood its valley is cut downward into the broad plain to a depth of nearly 200 feet. As one stands on a prominent point on either side of the valley and looks up and down the stream, it is easy to see the line of light-colored mortar beds lying almost at the summit of the bluffs, with the darker colored shales and sands beneath. A more careful examination shows that for many miles along the stream relatively firm rock covers the topmost part of the bluffs, and it is largely to this that the precipitous character so pronounced on either side of the river around Arkalon is due. Beneath the mortar beds are found masses of sandy clay, which constitutes the main mass of the bluffs. At other places, particularly along some of the tributaries of Spring Creek near Meade Center, the mortar beds in a well-developed form are found on low ground more than 100 feet below those capping the hills a mile or so away, with no connection between them.

During the last two years the Kansas State Board of Irrigation has

sunk twenty wells in western Kansas, the greater portion of which are confined to the Tertiary. One of the provisions in the contract for the drilling of each well was that a carefully selected and accurately labeled suite of samples should be preserved and delivered to the board, such samples to be taken with sufficient frequency to accurately represent the character of the material passed through. These samples from the different wells were turned over to the writer by the Board of Irrigation and have been carefully examined. This is the first time it has been possible to examine the Tertiary materials at any considerable depth below the surface, except where they are found along the bluff lines of the various drainage streams. They are therefore of more than ordinary importance, and are worthy of notice in this connection.

It was found that little relation existed between the distance from the surface and the size of the gravel. Gravel beds of a considerable degree of coarseness were frequently found near the surface, and the finest sand and clay and silt were not infrequently found near the base of the Tertiary. There was such an irregularity of position shown with reference to any one material, and such a lack of definite relation between the different kinds of material, that it seemed as though but little if any dependence could be placed in any older classification.

In studying the physical properties of the Tertiary it is necessary to emphasize the statement that the so-called mortar beds are simply the sand and gravel and clay materials cemented usually with calcareous cement. The real stratigraphic conditions probably do not depend upon the presence or absence of cementing material, but rather upon the continuity of beds of like material. A stratum of gravel which is not cemented should be considered as important as though it had chanced to have its individual constituents held together by a cementing material of some kind. Yet in our study of the subject we are usually inclined to erroneously regard the beds which are cemented into a firm rock as more important than softer materials. It has been suggested by the writer that the formation of the cementing material has occurred since the deposition of the beds, and that it represents a process of weathering and desiccation still in progress. The ordinary weathering agents produce calcium carbonate near the surface, which is changed to the acid carbonate by rain water containing carbon dioxide washed from the atmosphere. It is then dissolved and carried downward until the dryness of the ground absorbs the moisture, precipitating thereby the neutral carbonate in whatever position it chances to be. As the beds of gravel and coarse sand more freely permit the passage of water through them than do other materials, naturally there would be a greater deposition of calcium carbonate in such beds.

It is doubtful if there can be any regularity discovered between the beds of the different kinds of Tertiary material in western Kansas. The mortar beds occur at all positions from the base to the summit,

as do also the sands and the clays. It has been found impossible to trace a bed of any one material very far in any direction. The records of the State wells add to this difficulty rather than lessen it. Neither does the assistance of paleontology lessen the difficulty, but rather increases it. In Phillips County the mortar beds contain skeletons of the rhinoceros and other animals, indicating that they should be correlated with the Loup Fork beds of Nebraska, and that they are about the oldest Tertiary beds in Kansas. To the southwest, in Meade County, a mass of conglomerate, which is as typical a mortar bed as can be found, is rich in fossil horses, llamas, elephants, etc., which paleontologists class as Pleistocene fossils. We therefore have the mortar beds with Loup Fork fossils at one place and with Pleistocene fossils in another, not only showing a lack of stratigraphic continuity, but showing that, after all, the so-called Tertiary of the State may be part Tertiary and part Pleistocene.

WATER SUPPLY OF THE AREA.

In the discussion of waters on the Great Plains it is well to bear in mind the different conditions under which water exists and the different classes into which the ground waters may be divided with reference to the geologic character of the materials in which they are found. Geologically we have two great classes of ground waters. One exists in the Dakota sandstones. It probably has a slow movement eastward, has principally been gathered from the rains falling in the eastern part of Colorado and farther to the north over areas where the sandstone is exposed at the surface, and in its eastward movement passes underneath the Benton, Niobrara, and other superior Cretaceous formations, so that in most places it exists under a pressure sufficient to cause it to rise an appreciable distance above the level at which it is found by the drill, giving artesian wells, or wells decidedly artesian in character.

The other water is that which is commonly known as ground water, sheet water, or underflow, as these expressions are understood by the people of western Kansas. It is confined to the Tertiary sands and gravels. It lies immediately above the impervious Cretaceous or Red Bed floor, and is sufficient in quantity to more than saturate the materials in which it exists for a distance above the floor varying from 5 to more than 100 feet. Throughout the greater part of the plains area, therefore, these two classes of water are separated from each other by all of the Benton and higher Cretaceous deposits. In rare cases, however, the Tertiary rests immediately on the Dakota sands, permitting the Tertiary water and the Dakota water to commingle. Could we exhaust the supply of either one to an appreciable degree, the other would doubtless be drawn upon and a movement would be set up from one into the other. Still, for convenience of discussion and clear presentation of the water conditions, it is desirable that the two classes should be discussed separately.

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