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uniformity, for the upper surface seems to be as level as it could be wrought with a plumb-line.
There are a few small grooves or scratches on the surface, and by means of a surveyor's compass I ascertained with a good degree of precision the direction, which was generally 27° east of north.
There were some exceptions, as can be seen in the illustration, which is an exact copy from the rock. The variation of the needle here is about 11° 45'. The whole process here seems to have been a smoothing one, with a few small pebbles, perhaps, in the bottom of the glacier.
The following illustration will show the character of the scratches, and the fact, also, that there are indications of two sets; the scratches crossing each other at different angles.
I will now quote two or three paragraphs from a memoir published in 1862, which had a very limited circulation, and is now out of print:
“ Near the mouth of the Elkhorn the sandstone presents much the same character as before described. At this point it reaches nearly to the water's edge, showing that the dip of the formations in this region is toward the northwest. Here formation No. 1 is at least eighty feet in thickness, about fifteen feet of carboniferous limestone being exposed beneath. The latter soon passes beneath the water-level of the river, and the sandstone occupies the country.
“ The bottoms along the lower Platte are quite broad, and extremely fertile, possessing a rich soil, and admirably adapted to the wants of the farmer. Fine crystal springs issue from the limestone banks; a sufficiency of timber skirts the river or clothes the bluffs; the climate is quite dry and healthy, and if it were not for the extreme cold of winter, this region would be one of the most desirable agricultural districts in the west.
“The timber of the uplands consists chiefly of ash, elm, oak, soft maple, boxwood, &c., while along the bottoms the cottonwood forms nine-tenths of the woodlands. The land, when in a state of nature, supports a most luxuriant vegetation, and when cultivated by the farmer, brings forth very abundant crops.
“The valley of the Elkhorn is similar to that of the Platte, and the land is at this time mostly taken up by the actual settler. The bluffs are formed of sandstone, No. 1, often presenting lofty vertical walls, which, from the yielding nature of the rock, are of great service to the Indian upon which to record his hieroglyphical history."
On my return to Bellevue, I passed over the upland prairie, several miles north of the Platte. Already nearly every valuable claim was occupied by the persevering pioneer, and, as far as the eye could reach, the plain was dotted over with farm-houses, giving it much the appearance of an old settled country, Very little timber, however, is to be seen, except that which skirts the small tributaries of the Platte. The soil upon which the surface is composed is of a rich vegetable mould, the result of the annual decay of a luxuriant vegetation, underlaid by a yellowish silicious marl, and is admirably adapted for the cultivation of all kinds of cereal grains, and for grazing purposes.
When the prairie turf is broken up by the plough, and a'lowed to decay, the land becomes like a garden. The soil is so loose that it is tilled with great ease, but, from this very fact, is liable to suffer extensively from the wash of the heavy drenching rains of May and June.
The crops of wheat, oats, and corn, in both of these counties the present year, show unmistakably the very great capacity of the soil, thirty-five to forty bushels of wheat, fifty to sixty of oats, sixty to seventy-five of corn per acre, being a no uncommon yield, and the present season there will be even more than the average yield of former years.
Grass is also fine everywhere, each acre averaging from one and a half to three tons per acre.
GEOLOGY OF NEBRASKA NORTH OF THE PLATTE RIVER.
With the exception of a small portion of Douglas and Sarpy counties, bordering on the Missouri and Platte rivers, the whole State of Nebraska north of the Platte river is underlaid with rocks belonging to the great geological eras, cretaceous and tertiary.
The cretaceous rocks make their appearance in their eastward extension in rather thin beds, capping the summits of the hills, and only the more compact layers, resisting the eroding effects of water or atmospheric agencies, remain to indicate its boundaries and extent. I am inclined to the belief that the rusty sandstones of the Dakota group once extended in full force directly across the Missouri into Iowa, and that the sandstones recently discovered by Dr. White on the Nishnabotna river form a portion of the series, disconnected only by the wearing away of the intervening rocks. There is no doubt that the greater portion of northwestern Iowa is underlaid by rocks of the Dakota group.
The green color on the geological maps of Nebraska in process of preparation will show the eastern boundaries of this group with accuracy. The limestones early begin to disappear north of the Papillion river.
At Sarpy's old trading post, near Bellevue landing, some thin layers of rock occur in the hills, and a thin seam of coal has been found, and at low water two or three layers of rock are revealed which can be made useful for building purposes.
At Omaha five to ten feet of limestones are revealed near the water's edge. The rock is grained to considerable extent; but from the fact that Omaha is almost entirely supplied with rocks and lime for building purposes from the Platte, we may infer that the quarries at Omaha are not extensive. The cost of stripping the vast thickness of superincumbent gravel and yellow marl at Omaha must render the working of this quarry very expensive.
The next exposure is at Florence, where the limestones are seen only at low water.
The last exhibition is at Rockport, near De Soto, where at very low water the limestones are seen at the edge of the river, but at neither of the localities above named are there quarries of any special value.
Along the Missouri bluffs there is no exposure of the underlying rocks again until we reach Tekama, Burt county. Here the nuclei of all the hills are sandstones and clays of the Dakota group. From Florence to Tekama, the bluffs or hills bordering on the Missouri are very rugged and high, but are composed entirely of drift gravel at the bottom, and a great thickness of yellow marl at the top-indeed, this yellow marl or loam is not unfrequently fifty to one hundred feet in thickness. It is so soft and yielding in its nature that little temporary streams flowing down the bluffs wear out immense gorges one hundred to one hundred and fifty feet in depth. The sides of these hills along the Missouri bottom, on the Iowa as well as Nebraska side, are often very steep with angle of descent of 30° to 40°, and I have seen vegetation clinging quite thickly to their sides when the descent was 50° to 55°, although the great geographer, Ritter, says that the grade at which it is possible for earth to cling is 45°. At Tekama are some exposures of the sandstones of the Dakota group, but mostly 80 soft and friable as to be of little value as building material.
In the absence of all other rocks the inhabitants quarry out the harder portions and use them. Underneath the sandstones are the usual variegated clays and sands, red, white, gray, and drab, with nodules of the sulphuret of iron. In the sandstones above there is quite a variety in the texture of the rock. Sometimes there are thin intercalations of clay; then little pockets, as it were, of clay enclosed in a thin shell of iron ; then the thin layers are oblique, as if the waters in which the sands were deposited were in currents, or in a disturbed condition. Indeed it would hardly be possible to describe all the varied conditions which
this rock presents. Between Tekama and Decatur, a distance of about sixteen miles, there are frequent exposures of the sandstones and clays, but none worthy of special notice until we reach the vicinity of the little town of Decatur, vear the border of the Omaha reserve. Here some harder layers of rock are exposed which are used for the foundations of buildings and other economical purposes. There is one layer of quartzite.
There are also thin seams of iron ore, which, when broken with a hammer, give forth a sound much like that from old pot metal. It is really pretty fair iron ore, but quite silicious and impure, and even if this ore was of the best quality, and in great abundance, there is no fuel in the county to render it of any value.
At the Blackbird mission, on the Missouri, eight miles above Decatur, the bluffs of sandstone are quite conspicuous, and often present very high mural fronts, upon which the Indians have carved many rude pictures, doubtless portions of their hieroglyphical history. At this locality are quite numerous layers from one to four feet thick, of a very compact massive quartzite, the hardest and most durable rock in the State. It has the appearance of a metamorphic rock, so very hard and close-grained is it. The harder portions have been quarried out and used for the construction of a very large three-story building for the mission school.
As the construction of several railroad bridges across the Missouri are contemplated, no rock in the State would be so unyielding and durable for abutments as this, providing enough of it can be found. It seems to assume a concretionary form in the sandstone, and is of very uncertain thickness and extent.
About two miles above the mission the hills are cut by the river so as to reveal vertical bluffs, the rocks of which, in the distance, have a yellowish white appearance, and from this fact are usually called chalk bluffs. The sandstone is massive, almost without stratification, and very friable and soft.
4. Yellow marl; recent; ten to fifty feet.
3. Eight inches of earthy lignite resting upon twelve inches of yellowish drab arenaceous clay, underlaid by eight inches impure lignite.
2. Massive yellow sandstone, with some thin intercalations of clay, soft and friable, readily yielding to the erosive effects of water, sixty to eighty feet thick.
1. Yellow plastic unctuous clay, toward the top becoming a grayish blue; contains flat argillaceons concretions two feet.
This is, perhaps, the finest and largest exposure of the rocks of this group along the river. The mural exposures of soft sandstone present good surfaces for the Indian to make use of to write his rude history, and on the chalk bluffs there are many of these hieroglyphics in positions totally inaccessible to the Indian at the present time. None of them now living know anything about them, and it is supposed that they must be very ancient, and that since they were made great changes must have been wrought in these bluffs by the waters of the Missouri. These markings are at least fifty feet above the water and fifty feet or more below the summit of the bluff, so that they must have been made before the lower portion of the bluff was washed away by the Missouri. It seems strange that none of these hieroglyphical writings which occur quite often on the chalk rocks of the Niobrara group, higher up the Missouri, are known to any Indians now living. Manuel's creek is called in Dakota language the creek where the dead have worked, on account of the markings on the rocks.
The above illustration conveys an idea of the sandstones of the Dakota group as they front the Missouri, and shows the wearing away of the material of the rock underneath during high water. This erosion is continued for a series of years until the superincumbent rocks fall down and are washed away by the river. Near the mouth of Omaha creek are some very high vertical bluffs of sandstone, from which some rock has been taken for building purposes. It is useful, since no better can be found in the vicinity. For a considerable distance
along the hills opposite Sioux City, beds of the gray quartzite are found, which are worked to considerable extent, and furnish a very good supply for the inbabitants. A few impressions of plants and a few fossil shells were found here. Near Sioux City, on the Iowa side of the Missouri, is a high cut bluff extending to the mouth of the Big Sivux river.
Here was formerly a large exposure of the rocks of the Dakota group, and these rocks exhibited well their variegated texture and composition. The color seems to differ, depending upon the amount of ferruginous matters in them. Only about twenty feet of the different layers are exposed, and only about five feet hard enough for building purposes.
This quarry has been wrought for twelve years or more, and at this time seems to have given out, for very little suitable building stone can be found, mostly loose sandstone and clay. In former years I have obtained impressions of dicotyledonous leaves, as salix, laurel, sc., with some fossil shells of the genera Pharella, Axinea, and Cyprina, which are either estuary or marine in their character.
Near the northern boundary of the Omaha reserve, traces of a whitish chalky limestone, almost entirely made up of the shells of a species of Inoceramus make their appearance on the high hills. This rock indicates the first appearance of the cretaceous division.
Number 3, or the Niobrara. In passing northward, as we continue up the Migsouri we find this formation becoming more and more conspicuous until opposite Sioux City it is 50 to 100 feet in thickness. It is of much value to this region of the country, on account of its qualities as lime, and it supplies a large district with that valuable material. Omaha is largely supplied with lime from the region of the Platte. Between Omaha and the northern boundary of the Indian reservation, a distance of eighty miles or more, extending southward to the Platte, near Columbus, there are five or six counties entirely destitute of limestone. This limestone of the Niobrara group becomes very valuable therefore, and it will be from this upper district that the counties underlaid by sandstones of the Dakota group must obtain their supply of lime. Number 2, or Fort Benton group, seems to be wanting until we reach a point near the mouth of Iowa creek. This is a thin bed, not over 40 feet in thickness at any one point, and is characterized by black plastic clay filled with beautiful crystallized sulphuret of iron. It is pretty well exposed below the mouth of Iowa creek, where the Missouri cuts the bluffs, and here we see all the rock in their order :
4. Yellow marl, a recent deposit.
3. Niobrara group, layers of white and yellow chalky lime, passing down into gray marly rock.
2. Black plastic clay, with hard layers, containing inoceramus, a species of Ostrea, like 0. congesta, remains of fishes, many crystals of sulphuret of iron, selenite, &c.
1. Dakota group, sulphuret of iron, fragments of wood, impressions of leaves, willow, laurel, &c.
Near the mouth of the Niobrara river the black shaly clays of the Fort Pierre group begin to make their appearance on the bills over the Niobrara division, so that within the limits of Nebraska proper we have four out of five of the important divisions of the cretaceous rocks of the west.
Near the mouth of Ioua creek there seems to be a bed of impure lignite in the Fort Benton group or in the transition between the Dakota and Fort Benton groups. This bed, which has been worked to a considerable extent, and the coal used by blacksmiths in this vicinity with some success, does not seem to be the same as that seen along the Indian reserve, which is undoubtedly in the sandstone of the Dakota group.
I am inclined to the opinion that this bed of lignite near Ponka City is a local
bed, or at least restricted in its geographical extent, and is the result of an accumulation of drift-wood in an estuary of the cretaceous sea.
I am informed that it is seen over on the Elkhorn river about 35 miles west of this point.
Mr. Clark tells me that he dug twelve or fifteen feet below this bed and struck another seam of coal much better than the one cropping out. The lower bed must be the one in the Dakota group. Lithologically it is impossible to draw a line of demarcation between these formations here. Number 1 passes so imperceptibly into number 2, and number 2 into number 3, that there is no break, and yet their principal characteristics are very distinct. The first is a sandstone; second, a black plastic clay; third, a chalky limestone; and yet I cannot tell the exact point where one commences and the other ends.
The impressions of leaves have ceased to appear before the close of the Dakota group. The sandstones of the Dakota group occupy the whole country along the Platte from the mouth of the Elkhorn to a point some twenty miles beyond the entrance of the Loup fork. The intermediate counties between the Missouri and Platte have very few exposures of rock of any kind, so that quarries in this region, even though the rock is of inferior quality, are much prized.
The tertiary beds which make their appearance along the greater portion of the Niobrara, and really occupy a very large portion of western Nebraska, do not furnish much good building-stone. In order that the general geology of all this region may be better understood, I will give a general section of the cretaceous and tertiary rocks of the Missouri valley, which was first published by Mr. Meek and myself in the proceedings of the Academy of Sciences at Philadelphia. I have made such changes as the present state of our knowledge of this region requires, which are not of great importance.
The accompanying profile, also, along the Missouri river, from Fort Benton to the southern line of Nebraska, will show the basin-like character of the geological formations, and especially the subdivisions of the cretaceous rocks, and their relations to the tertiary.