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The McPherson Equus Beds
by Erasmas Haworth and J. W. Beede
Contents
Location
[Note: Mr. Beede did the greater part of the field work indicated in this paper.]
There is a formation of considerable economic and scientific interest located in McPherson, western Marion, Harvey, and eastern Reno counties. A large channel is carved out of the Permian shales and, in the northern part, Dakota sandstone. Its eastern limit, Plate XLV, is a line trending north and south along the west side of Sand creek to a place a few miles north and west of Lehigh, Marion County. Here it turns westward about twenty miles, then northward to the Smoky Hill river. Its western boundary, beginning at Smoky Hill river, runs south just east of Edward's creek to the Little Arkansas river, south of which the sandhills seem to encroach upon its area. It is well shown in the wells at Halstead and in all probability extends south to the general Tertiary or Pleistocene area along the Arkansas river. The "Tertiary grit" referred to by Professor Hay, just east of Wichita, is probably all outcrop of this formation, as on the margins of the area, and the isolated patches, the sand is imbedded in a limy matrix which resembles the "Tertiary grit" farther west. [Bulletin 57, U. S. Geological Survey, p. 34 and fig. 9.]
Over the deeper portions of the channel and well to its western edge lies a chain of lakes and basins extending from the large basin two miles west of McPherson to the Arkansas river south of Patterson. The area north of the Little Arkansas river is about eight hundred square miles. South of it, it is probably over one hundred square miles, exclusive of the sandhills.
Topography
The rough surface of the Permian to the east, the Dakota to the north, and the peculiar topography of the sandhills to the southwest, form a marked contrast to the monotonously level surface of the Equus beds area. There are several places where one may travel three or four miles without rising or descending twenty feet. Along the east and west section lines two miles north of McPherson one may travel ten miles without passing a sag of more than twenty feet. As a rule there is just slope enough to the surface for good drainage, while occasionally the water stands in lakes and basins in slight swales in the surface. The largest of the lakes is Lake Inman, ten miles southwest of McPherson. The largest basin is nearly three miles in diameter, and is situated two miles west of McPherson.
The divide between the Arkansas and the Smoky Hill river passes through this area and averages a little more than 1500 feet above sea level (U. S. Topographic Sheets). The Arkansas river at the southeastern limit is 1290 feet, a fall of 200 feet in sixty miles. The Smoky Hill river, at its nearest approach, is within four miles of the divide, but its bed is nearly 200 feet below it. The Little Arkansas river drains the entire area of the Equus beds except a very small portion north of the divide, drained by the Smoky Hill, whose small tributaries are rapidly cutting into the divide, and will cause it to migrate farther south in the course of time, as the streams on the south are already at their base level and are not carrying the soil away to any considerable extent.
Structure
These beds consist of alternating layers of sand and clay with a stratum of "volcanic ash" in part of the northern area. Near the bottom of the deepest part of the channel there is a heavy stratum of gravel, as shown in sections 1, 2, and 3, figures 1, 2 and 3 of Plate XLVI, which pass through McPherson, Harvey county, and Halstead respectively. This bed lies at a depth of 140 to 150 feet or more at McPherson and contains an abundance of water, as it does wherever it is found. The upper part of the gravel stratum grades into a stratum many feet in thickness, which is partly argillaceous and partly arenaceous, sometimes containing isolated sand beds, or at least sand beds of great irregularity, and which contain very little water. The upper surface of this stratum is nearly on a level with the rim of the deeper channel (see sections referred to above). Over this and also extending over a very slightly undulating Permian floor for fifteen miles to the east is a stratum of sand varying in thickness from 30 feet (at McPherson, according to Prof. S. Z. Sharp) to 3 feet in other places farther east, but averaging 6 or 8 feet in thickness. This stratum also contains a good supply of water. It covers nearly the entire area of the Equus beds except perhaps a portion to the north. The uppermost stratum is composed of clay varying in color and texture. It covers the entire area and is from 10 to 35 feet in thickness. Within this clay layer in the northern part of McPherson County is a stratum of volcanic ash from 18 to 24 inches thick.
Nodules of calcium carbonate are frequently found in both the upper and lower stratum of clay. As a rule they are very irregular in form, but generally show a slight roundness of form. Some of these are quite hard, while others are very soft, as is the case at the McPherson sand pit on the Boggs farm two miles southeast of the city, where it is 20 inches thick in places. A specimen of this was submitted to Dr. G. P. Grimsley, who states that it is "one mass of small prismatic crystals with pyramidal terminations, with strong double refraction and no cleavage. They effervesce with acids and are crystals of aragonite (CaCO3), the orthorhombic form of calcium carbonate." No structure could be determined in the hard nodules. Doctor Grimsley pronounces the volcanic ash as "glass grains or flakes, fine and angular, some of which are feebly doubly refracting." A specimen of the sand was examined by him and found to be "rounded quartz grains with a number of angular ones." Specimens of Dakota sandstone and sand from Dakota sandhills were also pronounced of the same character, except differing in fineness. As no feldspar grains were found in the sand it would seem to have originated from the Dakota sandstone rather than to belong to the Tertiary sands at the west, or the glacial sands farther east.
The fossils of this formation are those of the Equus beds according to Dr. S. W. Williston. Those reported are (Udden, American Geologist, vol. VII., No. 6, June 1891.): Megalonyx, subsequently described as M. Leydeyi, Equus major De Kay, Spherum striatum Lam., S. Sulcatum Lam., Pisidium abditum Haldeman, Anodonta sp., Valvata tricarinate Say, and Gammaria sp.
It may be well to note here the physical characteristics of the rocks through which the valley containing the Equus beds and the present valley of the Smoky Hill river are cut. The former is in the main cut through soft, easily eroded Permian shales. The northern portion has been cut through a considerable amount of Dakota sandstone. The 200 or more feet removed north of this is largely Dakota (60 feet of Permian). The section at the Smoky Hill buttes will give a good idea of the general nature of the rock: A few feet of soft sandstone at the bottom, then 110 feet of shale, 200 feet of sandstone (now soft and friable), and a covered slope constitutes the section. The latter is probably sand, as the water percolates through it freely down to the top of the shales, where it breaks forth as springs. The upper part of the 200 feet is a comparatively hard sandstone 10 or 12 feet in thickness. Though the texture of the materials in the above section may vary, and does for different localities, the hardness and friability remain practically constant, making the material admirably suited for rapid erosion. This is true of the entire eastern portion of Saline and McPherson counties.
Origin
Two papers have been published on this formation, one by Professor Udden (Loc. cit.) the other by Professor Sharp [Bulletin Kansas State Board of Agriculture, quarter ending March 13, 1894, pt. 2, pp. 26, 30]. The latter expresses the opinion that it is of glacial origin. It was thought that the ice formed a dam across the Kansas river somewhere below and that the water, backing up to Salina, burst through the divide at the place where the north end of this formation is situated. In evidence of this theory he cites some boulders on Battle Hill as being of glacial origin, dropped or deposited by a stranded iceberg from the terminus of the ice sheet.
The boulders on Battle Hill, Battle Hill township, McPherson County, are not the rounded quartzite boulders of the moraine, but cross-bedded sandstone of the Dakota formation lying nearly in place. They are about 3 feet thick, hard and angular, some of them quite large. There is also an absence of other moraine material, which a melting iceberg or ice sheet would certainly have deposited. Rocks very similar to these may be seen in place a mile southeast of Salina, two miles north of Twin Hills, (northeast corner of Delmore township, McPherson County,) and four miles west of Battle Hill. Here the soft, almost incoherent sandstones, removed from beneath the hard sandstone, which allowed the large blocks of the latter to gradually tip and tilt over the surface of the hill, and some of them have worked their way down its sides some distance. In one of these, on the northeast face of the north hill, the lower part grades into brownish Dakota sandstone.
The elevation of Battle Hill is 1550 feet, which is about the same as the elevation of the highest of the deposits of the Equus beds. The elevation of the terminus of the ice sheet in Shawnee and Wabaunsee counties, so far as definitely located, is about 1050 feet, or not over 1100 feet above sea level. [All elevations based upon U. S. Topographic Sheets.] The planation of the surface is so slight that were it not for the small amount of material left by the glacier it would have been difficult indeed to recognize the former existence of glaciers in that portion of the state. Consequently it seems probable that the ice sheet was comparatively thin at its southwestern portion, the limit of which is even yet not entirely known. The elevation of the divides between the Kansas and Marais des Cygnes rivers south of Topeka is 1100 feet. This is over 400 feet below the boulders at Battle Hill, or the more elevated deposits of the Equus beds. How far up the Kansas river the loess is found is not known, but it probably does not extend above Topeka as far as to the summit of the flint hills in Wabaunsee County. It seems probable, therefore, that the waters of the Kansas river would have flowed around the foot of the glacier to the east of these hills rather than to rise to an elevation of 1550 feet, which is even higher than the divide between the Kansas and the Neosho river in the flint hills of Wabaunsee County, which are now considered to be quite above and south of the terminus of the ice sheet.
Professor Udden in the article above referred to suggests that the waters which deposited these beds must have connected with another body of water in the valley of the Smoky Hill river to the north, and states that the river has cut its channel through these deposits.
The elevation of the McPherson divide at its central point is a trifle over 1500 feet. To the southward at a distance of thirty eight miles the Arkansas river flows at an elevation of a little over 1400 feet, or a fall of 100 feet in thirty eight miles. The bed of the Smoky Hill river eight miles farther north is 1300 feet. The city well at McPherson, starting 1475 feet above sea level, was put down 150 feet (the present water supply is taken from a depth of 140 feet) without striking the bottom of the deposit. This makes the bottom of the well 25 feet above the bed of the Smoky Hill river two miles south of Lindsborg, or about the same level as the bed four miles east of Marquette, still on the northern boundary of the Equus beds. The present elevation of the Arkansas river at the mouth of the Little Arkansas is 1290 feet. This difference of elevation of the two rivers is party due to the fact that the Smoky Hill flows nearly east across the north end of the beds while the Arkansas flows southeast, making its distance greater in crossing the southern end of the formation. The relation of the two river beds and the records of the McPherson and Halstead wells is shown on section 4, figure 4, Plate XLVI. The section begins at the mouth of Sharp's creek and passes along the western edge of McPherson and a trifle east of Halstead to the Arkansas. It will be seen at a glance that the two rivers are at the same level at the extremities of the elevation and that the gravel in the McPherson well lies in exactly the same level, while the gravel of the Halstead well passes below it. The fact should also be borne in mind that the Arkansas river has reached its base level and filled its channel to some extent, though how much is not definitely known.
The above figures would seem to indicate that at one time the Smoky Hill river ran south instead of north and emptied into the Arkansas. But it is difficult to understand why it should have excavated so great a channel and covered so wide a flood plain here and so narrow a valley west of Marquette. However, the encroachment of the sandhills on its southern area may offer a slight suggestion as to the partial choking of the southern outlet causing more rapid deposition to the north, and thus elevating the channel and widening the flood plain.
But there are other facts which seem to detract from this explanation of the origin of these beds. If the Smoky Hill river at one time flowed south into the Arkansas, then one of a number of conditions must have obtained.
First: The Saline could have received a short tributary from the southwest, occupying the position the Smoky now has throughout that part of its course above Salina where it flows north. The source of this tributary could have gradually migrated southwestward by natural processes until it captured the Smoky at the point of the big curve in the present river. The accumulation of sand above referred to along the northern side of the Arkansas would have assisted in this by elevating the mouth of the old Smoky. But unfortunately for this view no part of its course south of McPherson is as high as the high McPherson ridge, which is 1550 feet above sea level near McPherson to the north. Were this ridge formed by the natural filling-up process in the old valley of the Smoky before its capture, we should find some evidence of a corresponding filling further up stream in the present valley and a widening of the valley corresponding somewhat with the wide valley now occupied by the Equus beds. No such filling or widening of the valley is noticeable. Further, at all points above the McPherson ridge the bottom of the channel must have been at least as high as the ridge, and a short distance away it must have been higher. At present one must pass upstream over thirty miles, to above Ellsworth, before the river channel has an elevation of 1550 feet. After the capture, on account of the Saline near Salina being so much lower than the Smoky in its hypothetical position, a rapid deepening of the channel would have occurred throughout a distance of from thirty to fifty miles above Salina, and a new flood plain, the present one, would have been formed. No such phenomena have been observed. The present wide valley above Salina also somewhat opposes this view, as it is difficult to understand how the short tributary supposed to have captured the Smoky could have produced so wide a valley, while its width and depth at present between Lindsborg and Salina seem altogether too great to have been excavated since the deposition of the Equus beds. The Smoky Hill buttes, Soldier Cap mound, Iron mound, and North Pole mound register the ancient elevation of the surface of Saline County, and indicate the removal of over 200 feet of material consisting of Dakota sandstone and shales and Permian shales, from the entire valley, which is nine miles wide in its widest place, including Dry creek valley. The valley between the Smoky Hill river and Dry creek is now largely covered with Pleistocene river deposits with occasional mounds of Permian shale rising to the surface. The average width of this valley is two and one half miles, over which the sand and clay average about 35 to 40 feet in thickness. The bed of Dry creek is about on a level with that of the Smoky Hill river, and during very high water in the latter its overflows its banks at Bridgeport and part of the water runs down Dry creek and empties into the Saline ri ver north of Salina.
Second: It may be supposed that at one time the Saline and the Smoky flowed south into the Arkansas, joining each other at the big curve in the Smoky south of Salina. In this case a short tributary to the Solomon occupying the position of the present Smoky between Salina and Solomon City would have been the capturing stream, tapping the Saline river near Salina, and ultimately causing the Smoky to flow up the old Saline channel from the point of confluence of the two streams to the point of capture. The whole valley of the Saline, therefore, must have been elevated' above the McPherson ridge and probably would have had a flood plain of considerable width, while the flood plain of the upper Smoky would have been about the same as above given in the first supposition. When the capture was made the great fall from this supposed elevation at Salina to Solomon City would have caused a rapid deepening of the channel in both the Saline and the Smoky, and new flood plains would finally have been formed along both streams, as already explained for the Smoky. No such conditions have been noticed along either stream. Further, the great elevation required for the Saline would have carried it across the uplands into the Solomon above Minneapolis. Neither does the character of the present valley between the mouth of the Saline and the mouth of the Solomon river appear to have been so recently a mere lateral to the Solomon only a few miles long.
Third: If the materials of the Equus beds were brought down from the west by the Smoky Hill river, or by any other stream, or if the materials are largely of glacial origin, then they should correspond closely in character with the recent river sands or with the glacial material. Almost every handful of sand gathered from the valley of the Arkansas, the Smoky, or the Saline, streams passing through the Tertiary regions of the west, is largely composed of feldspar gravels, and frequently fragments of other rock-forming minerals are seen. Likewise the sands of the lower Kansas river valley which are so largely of glacial origin have a great abundance of feldspar gravels. But the sands of these Equus beds so far as examined by Doctor Grimsley seem to have no feldspar whatever. This strongly implies that they are obtained directly from the Dakota sandstone, as that rock is almost if not entirely free from feldspar gravel in this part of the state.
At present it must be admitted that no satisfactory explanation of the origin of the Equus beds channel, nor of the agency for the deposition of the materials, has been advanced. A further study of the problems involved is in progress.
Economic Interest
This strip of country is particularly fertile and very valuable farm land. The soil seems to possess nearly all the peculiarities necessary to the growth of the various farm products. It is so level that it can almost all be cultivated, the uplands being about as good as the bottom lands. The water supply is almost ideal. Over the entire eastern portion at a depth of 18 to 30 feet, pure, soft water is found in good supply. The soft arenaceous texture of the clay above the sand beds containing the water makes well digging easy. Over the western portion the wells vary from 40 to 150 feet in depth, but the water is always good and there is an "inexhaustible" supply of it. The wonderful amount of water contained in this lower gravel bed of small extent is remarkable. A glance at section 4 will suggest that the supply may be traced, upon further investigation, to the Smoky Hill and Arkansas rivers.
The streams have no native timber on them worthy of note, but on the uplands and valleys cottonwoods and other trees thrive wherever planted, their roots penetrating the clay to the sand for water. This is in marked contrast to the country just to the east, where the Permian shales are the surface rock. Here the cottonwood trees grow to be fair sized trees and then die.
The rainfall is sufficient on this area to produce a fair crop almost every year. The area covers over nine hundred square miles and may be said to be the richest farm land of any area of its size in Kansas, and its inhabitants the most thrifty.
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Kansas Geological Survey, Geology
Placed on web Jan. 20, 2018; originally published 1897.
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