It is, therefore, evident that this formation is very widely distributed, perhaps even east and west from one ocean to the other.

FORT BENTON GROUP.

This group bears the above name from the fact that it is largely developed in the vicinity of Fort Benton, near the sources of the Missouri river. In ascending the Missouri, it is first seen in thin outliers below the mouth of Big Sioux river, and on the Big Sioux six miles above its mouth. It is characterized as a dark leaden gray plastic clay, but when saturated with wafer it is of a black color.

A few fossils have been found at various localities, as Inoceramus problemat icus, Ostrea congesta, Ammonites, Serpula, &c. Near the mouth of Iowa creek there is the best exposure of this group, as well as groups above and below.

3. Gray and light yellow calcareous marl or chalky limestone, with great numbers of Inoceramus problematicus, Ostrea congesta, and remains of fishes. Niobrara division, 40 to 50 feet.

2. Dark plastic clay, with abundant remains of fishes, I. problematicus, O. congesta, Ammonites peracutus, Serpula tenuicarinata, and a species of oyster, like O. congesta. Fort Benton group, 30 to 40 feet.

1. Variegated sands and clays of Dakota group, 15 to 20 feet above water's edge; impressions of leaves of willow, laurel, and many crystals of sulphuret of

iron.

The beds of the Fort Benton group are widely distributed throughout the west, but in no portion has it revealed any useful minerals or economical rocks of any kind, to my knowledge. The black plastic clays may be rendered useful at some period, but it is quite doubtful. They are everywhere filled with sulphuret of iron.

At the locality where the above section was taken I obtained some of the finest specimens of crystallized sulphuret of iron I have ever seen. There were also many species of selenite. So far as I know, this formation does not exert

any favorable influence on the country.

The beds of impure coal near the mouth of Iowa creek are very interesting in a geological point of view. At no other locality do I know of the existence of any seams of carbonaceous matter. This coal is too impure and contains too much sulphuret of iron ever to be made available.

NIOBRARA DIVISION.

In many respects this is the most interesting and most valuable group of the cretaceous rocks in the west. Its principal character is a gray or light yellow chalky limestone; much of it is so pure as to make good chalk for commercial purposes.

It would also be useful, doubtless, as a fertilizer. In ascending the Missouri it is first seen in thin outliers on Pilgrim's Hill, a portion of the Omaha reserve. It then grows gradually thicker as we ascend, and south of Dakota City, in the hills, it becomes ten to twenty feet thick. At Ponka City, St. Helena, and mouth of the Niobrara it is exposed fifty to two hundred feet in thickness, exhibiting a great variety of color and texture.

All along the Missouri this rock is much used for the construction of buildings with success. The fact that so large an area of country exists below the first appearance of this formation destitute of any rock for lime must render this group of much economical importance to the settlers. Its soft, yielding nature gives rise to long ranges of precipitous bluffs along the river.

It is easily cut into innumerable ravines by the temporary streams, and these bluffs often present the appearance of a series of cones.

This formation extends up the river to the foot of the great bend, where it passes beneath the water level. The fossils in this group are few in the number

of species, but the individuals are abundant. Layers of considerable thickness are mostly composed of the shells of Inoceramus problematicus and Ostrea congesta.

Fish remains of great perfection and beauty also are found. Only a few good specimens have ever been taken from the rock; but the myriads of fragments, as bones, scales, and fins show that they existed in great abundance in the cretaceous seas. The connection of this group with the Fort Benton group below is quite plain, there being no line of demarcation in most localities. At St. Helena, however, the transition is abrupt, passing directly from the black plastic clays of the one to the yellow chalk of the other.

This fact seems to me to show clearly that the grouping of these formations in the manner already done is correct.

Between the Dakota group and the group above there are transition rocks at different places which obliterate any abrupt break, while at other localities the break is evident.

All our investigations show more and more clearly that in the cretaceous series of the west there are three divisions paleontologically, and five groups lithologically.

The Niobrara division undoubtedly extends all along the mountain elevations; but it seems to possess an intermediate character between Nos. 2 and 3, as seen on the Missouri river, so that it is difficult to decide to which the rocks belong, the Ostrea congesta being common to both. This formation, like the Dakota group, extends across the country, in the form of a belt or zone, southeast and northwest.

It is found extending north high up the Big Sioux, Vermillion, and James rivers, in Dakota Territory, and southward into Kansas and New Mexico.

FORT PIERRE GROUP.

This formation is most largely developed from the Great Bend to a point 200 miles above Fort Pierre. It begins to make ite appearance on the summits of the hills near the mouth of the Niobrara, and soon gives the character to the country. The surface underlaid by this formation looks barren and arid, and is really the commencement of the reputed sterile belt southward. It is composed mostly of laminated shaly clay, is usually quite uniform in its composition and texture, and contains so much alkaline matter that it prevents the growth of most plants except those that are peculiar to such soil.

The hills above Fort Randall, on both sides of the Missouri, have a barren, black appearance, and are often called the "burnt hills" by the voyageur. Sometimes numerous masses of selenite are scattered over these hills, which glistening in the sun has suggested the name of the " shining hills." The burnt appearance is undoubtedly due to the decomposition of iron pyrites by exposure to the atmosphere or water.

When much vegetable matter exists in the beds, as in the Niobrara group at one locality near Bijoux Hills, and in the lignite tertiary beds, it takes fire and bakes the superincumbent beds of rock, so that the remains look in the distance like a pile of ruins.

Inasmuch as the rocks of the Fort Pierre group do not occupy any considerable portion of the State of Nebraska, I shall not discuss their character to any extent in this connection. It makes its appearance only in a few localities, as an overlapping rock south of the Niobrara river, and therefore exerts comparatively little influence on the country below that point.

The eroded materials of the rock are no doubt mingled greatly with the superficial deposits which cover the northern portions of the State. It is sufficient to remark that it occupies a vast area in the territories of the northwest, and that it has yielded many most interesting organic remains. It is in many instances

Fort Union or great

lignite group.

Wind river

deposits.

White river group.

Loup river beds.

Names.

intimately blended with the group above, which we have designated in the section as the Fox Hills group. This latter group is not found in Nebraska at all, but is seen in its typical condition on a conspicuous and quite fertile ridge of land between the Big Cheyenne and Cannon Ball rivers, higher up on the Missouri. It extends from the eastern side of the Black Hills across the country northeastward. These beds give a more cheerful appearance to the country; there is more timber, and springs of pure water are common. It is also full of organic remains of great variety and beauty. This is an arenaceous deposit for the most part, and has doubtless contributed its share toward giving fertility to the Nebraska soils.

TERTIARY FORMATIONS OF NEBRASKA.

These formations in the valley of the Missouri present features of the highest interest to the geologist, and perform a prominent part in revealing the geological history of the west. They mark the dawn of those internal forces which culminated in the present physical configuration of the vast area between the Mississippi and the Pacific ocean. So far as known, only the more modern tertiary deposits of the fourth basin occur within the limits of the State of Nebraska. But in order that the relations of these deposits may be shown to those of the cretaceous period, and the connection of the basins with each other, I shall give a brief description of them all in their order. The following general section of the tertiary deposits of the northwest will show their extent and relation to each other in order of time:

The details of all these formations will be discussed more fully in the final report.

Commencing with the oldest of these tertiary basins we have

1st. Judith river basin, which is located near the entrance of the Judith into the Missouri; and is separated by the latter river into two nearly equal portions. It covers an area of about fifteen to twenty miles east and west, and forty miles from north to south.

This basin is one of much interest, as it marks the dawn of the tertiary period in the west, by means of the transition from near brackish to strictly fresh water types It is also remarkable for containing the remains of some curious reptiles and animals, reminding the paleontologist of those of the Wealden of England.

2d. The great lignite basin, which occupies all the country from Heart river to the Muscle Shell-most of the valley of the Yellowstone-extends for an unknown distance northward into the British possessions and southward at least to the North Platte, where the beds of the fourth basin overlap, coming to the surface again at Pike's Peak, and extending to Raton pass, in New Mexico.

The limits of this great basin have not yet been determined. Although not known to occur within the present defined limits of the State of Nebraska, it will undoubtedly have an influence on the prosperity of the State, on account of the extensive lignite beds which occur in it. Along the Missouri and Yellowstone rivers are forty or fifty beds of lignite, varying from one to seven feet in thickness, of various degrees of purity.

In the vicinity of Denver, Colorado Territory, according to Mr. E. L. Berthord, civil engineer, there are several beds of lignite twelve to eighteen feet in thickness, which must furnish an immense mass of fuel, which will soon become accessible to the people of Nebraska through the Union Pacific railroad:

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Our coal seams extend, to my knowledge, sixty miles due east from Pike's Peak, in one direction, south to Raton mountains and the Raton pass, and northward to near Denver, on Cherry creek, and on the west side of the South Platte as far north as the Cache la Poudre, and to the foot of the main mountain range. Here, in Golden City, we have a large outcrop of coal, which has been opened successfully, and which inclines toward the town. In one of the newly opened mines on the same outcrop of the Golden City vein, which lies north on Coal creek, about nine miles from Golden City, I saw, in 1861, the trunk of a tree taken out of the eleven-foot vein then opened and mined, which trunk, though turned into coal of a good quality, exhibited carbonized bark, knots, and woody fibre, with concentric rings of growth, such as our dicotyledonous trees plainly show; indeed, one of the miners remarked that, from the bark, and the grain and fibre of the coal, it was very much like bitter cottonwood, (Populus angulata,) examples of which grow close to the mine.

In 1862, while on a scout east of Pike's Peak sixty-five miles, I found a bed of coal almost identical with the Golden City bed, nine feet thick, lying almost horizontal, with bluffs one and a half miles north, containing fine specimens of belemnites.

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Again, in November, 1866, I went northeast of Golden City to see the coal beds on Rock creek, sixteen to nineteen miles distant. I found beds of coal fourteen to eighteen feet in thickness, almost horizontal, or dipping eastwardly at a small angle; above them, ferruginous sandstone, and vast beds of bog-iron ore and clay iron-stone, in nodules, with numberless fragments of bones. In the sandstone I have obtained fossils like hippurites, but in none of the beds so far have I found a single marine or fresh water shell, with the exception I have before mentioned.

"Everything that I have so far seen points out that the coal is either cretaceous or tertiary, but I believe it to be tertiary, or of the same age as the coal near Cologne, on the Rhine; but I am perplexed at the inversion of the dip of the

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with these coal, sandstone, and the iron ore, which here incline toward the mountains instead of away from them, and nothing else that I have observed can compare tilted-up beds.

"I have not time now to follow up this subject, nor to give you all the data that I have gathered so far; I shall report to you in full in regard to the points you mention, but will give you, as soon as time permits, a full report, with elevations, profiles, &c.; also some specimens to prove the relative age of the strata shown in my sketch."

In the newspapers may be seen advertisements of coal for sale, so much per ton delivered, and so much at the mine.

This coal, as well as that at Raton Pass district, is of tertiary age, and it is questionable whether the true coal measures furnish any coal in any portion of the Rocky mountain region.

3d. The Wind river deposits, which occupy an area about one hundred miles in length and forty to fifty in breadth.

These deposits are located between the Wind river and Big Horn mountains, and are of no economical importance.

4th. The basin of the Mauvaises Terres, or bad lands of White river, cover a large region, at least 100,000 square miles, and from isolated patches on both sides of the Missouri river, I would infer that this great fresh water lake must have spread over 150,000 square miles. It is this latter formation which covers the greater portion of western Nebraska. The colors on the geological map will show the area. The cretaceous beds occur along the Niobrara for eighty to one hundred miles above its mouth; then the loose sandy and marl beds of the tertiary basin overlap them. From thence to the source of the Niobrara, about All of Nebraska three hundred miles, the river runs through the tertiary deposits only. This stream forms the northern boundary of the State. west of longitude 101° is occupied by the sands and clays of the fourth basin. The "bad lands of White river" are so called because, being composed of indurated sands, clays, and marl, they have been so cut up into ravines and cañons by streams, rains, and other atmospheric agencies as to leave cones, peaks, isolated columns, and towers, presenting the appearance in the distance of a gigantic city in ruins.

It is so exceedingly rugged and difficult of access that it is only within a few years that any route but the Laramie road, which runs through the middle of Of late years it has been shown by various exthem, was considered passable. peditions, both public and private, that any portion of the great west can be traversed with teams, if necessary.

The cretaceous beds of the Fort Pierre group extend along White river from its entrance into the Missouri, except about fifty miles near the forks, where the White river tertiary overlaps them.

Even now some isolated patches of tertiary are seen, as Medicine and Bijoux Hills.

All the intervening From the forks or the junction of Little White river with the larger streams the tertiary beds occupy the whole country to its source. country between White and Niobrara rivers is covered with the sands, clays, and marl of the White river deposits, but along portions of the Niobrara and south of that river the lower sands of the Loup river deposits make their apHere we find a singular region of country called the "Sand Hills," pearance. which occupy an area of about twenty thousand square miles. These hills lie mostly between the Niobrara and the Platte, though a portion of them extend northward of that river.

On the south side of the Niobrara the Sand Hills commence at Rapid river and extend westward about 100 miles. Along Loup fork they commence near the forks or the junction of Calamus branch with Loup fork.

The whole surface is dotted over with conical hills of moving sand. These