that of an arid country. Dwarf pines, piñons, and sage-brush abound, to the almost entire exclusion of other trees or grass. Traveling down White River this character is again found to change. A new series of bluffs, occasioned by heavy superincumbent strata, gives rise to the formations of deep cañons. For forty-five miles the party followed the cañon of the White, which no doubt is analogous to that of the Green, and probably closely resembles that of the Colorado in its detail features. Vertical walls enclose the narrow river-bottoms and the slopes of the higher portions are ornamented by thousands of curiously eroded rocks. Monuments of all kinds and figures that can be readily compared to those of animated beings enliven the scenery, which otherwise would be very monotonous. Two thousand to three thousand feet may be stated as the height of the walls inclosing the White River. Geologically speaking, the district is one of singular uniformity. Traveling westward, the older formations, reaching back as far as the Triassic, were found. This is followed by Cretaceous, which in turn is covered by Tertiary. About three quarters of the region surveyed was found to contain beds belonging to this period. Owing to the lithographical character of the strata, water was a rare luxury in this region, and men and animals were frequently compelled to look for springs. Farther west still, the Green River Group sets in, forming those numerous cañons of which that of the White River is

one.

Having completed their work by October 14th, the party marched eastward through Middle Park, and after twelve days of rain and snow reached Boulder City, Colorado.

The field work of the Yampah division during the past season was principally confined to a district of Northwestern Colorado lying between the Yampah and White rivers, and between Green River and the subordinate range of mountains that lies west of and parallel with the Park Range. The area is embraced between parallels 39° 30′ and 40° 30' and meridians 107° 30' and 109° 30'.

The party consisted of Mr. G. R. Bechler, topographer directing, accompanied by Dr. C. A. White, the well-known geologist. They proceeded southward from Rawlins Springs, a station on the Union Pacific Railroad, on August 6th, toward their field of labor. From Rawlins Springs to Snake River, a distance of eighty miles, table-lands form the chief feature of the topography, while from Snake River to the Yampah River the surface is

more undulating and thickly covered with sage. Between the Yampah and White rivers, a distance of fifty miles, the country is mountainous; and on the divide between the Yampah and White rivers the elevation is eight thousand to nine thousand feet. Mr. Bechler, after having formed the geodetic connection with the work of previous years, concluded to finish the more mountainous portion of the area assigned to him, which began in the longitude of the White River agency and extended westward to about 108° 10'. Here the party found water and grass in abundance, with one exception.

The plateau country, however, was so destitute of water and so cut up with dry gorges or cañons with scarcely any grass or timber of any kind, that traveling was rendered very difficult. The party therefore made White River its base of supply for water and grass, making side trips among the barren hill-tops or plateaus in every direction.

From the Ute Agency, which is located approximately in latitude 38° 58′ and longitude 107° 48', the White River takes an almost due west course for fifteen or eighteen miles, most of the way through an open valley with here and there narrow gorges. About fifty miles from the agency, the river opens into a broad barren valley, with only here and there scanty patches of vegetation. Soon after, the river enters a deep cañon with vertical walls one thousand feet or more in height which continue to increase in depth until the river flows into the Green River.

The Yampah or Bear River occasionally deviates from a westerly course only for a few miles. Like White River it flows through a plateau country which rises gently from the river, back for a distance of about eight miles. South of the river lie the Williams River Mountains, which have a gradual slope to the north. Williams Fork, flowing from a southeastern direction, joins the Yampah River. West of the junction, the Yampah traverses the country more or less in a cañon, occasionally emerging into an open grassy valley, then enters a deep cañon, cuts through the Yampah Mountains, when it joins with the Snake River. The place of junction resembles a fine park surrounded on all sides with eroded terraces and plateau spurs, that rise by steps to the divide on either side. This park is about eight miles in length from east to west.

After leaving this park the river enters a huge fissure in the mountains, where it remains until, completing its zigzag course, it joins the Green River in longitude 109° 40' and latitude 32° 00'.

After the junction with the Yampah, the Green River continues in a cañon for fourteen miles where it passes through the picturesque palisades of Split Mountain into an open broad valley, longitude 109° 15', latitude 40° 28', from which point it takes a southeast direction through the Wamsitta Valley, where it unites with the White River.

Into both White and Yampah rivers, numerous branches extend from either side, forming deep cañons the greater portion of their length. We may say in brief, that the sides of the valleys expand and contract, at one time forming the beautiful grassy valleys which in olden times were celebrated as the favorite wintering places for the trappers, or contracting so as to form narrow cañons or gorges with walls of varied height.

The walls of Yampah Cañon average about one thousand feet, while the mountains receding back to the northward attain an elevation of forty-two hundred feet, and the highest point of the plateau on the south side is thirty-four hundred feet above the river level.

Of the plateaus between White and Yampah rivers, Yampah Plateau is the largest, and occupies an area of four hundred square miles. The surface of the summit is undulating and on the south side it presents a steep face, several hundred feet in height, covered with débris, rendering it almost inaccessible. This plateau is covered with excellent grass and gives origin to numerous springs, all of which dry up within a short distance of their source. As a whole, this district is very arid, barren, and almost entirely destitute of tree vegetation.

The total number of stations made by Mr. Bechler in the district assigned to him was forty, and the entire area about three thousand square miles. Barometric observations were made whenever needed, and about two thousand angles of elevation and depression with fore and back sights, so that the material for attaining the correct altitudes is abundant.

The rocks of this district embrace all the sedimentary formations yet recognized by the investigators who have studied the region that lies between the Park Range and the Great Salt Lake, namely, from the Weber Quartzite (which underlies the Carboniferous) to the group or latest Tertiary, inclusive. Not only has the geographical distribution of these formations been mapped, but all the displacements of the strata have been traced and delineated. The last-named investigations bring out some interesting and important facts in relation to the orographic geology of the region, especially as regards the eastern termina

tion of the great Uinta uplift and the blending of its vanishing primary and accessary displacements with those of the north and south range above-mentioned. Much information was also obtained concerning the distribution of the local drift of that region, the extent and geological date of outflows of trap, etc.

The brackish water beds at the base of the Tertiary series, containing the characteristic fossils, were discovered in the valley of the Yampah. They are thus shown to be exactly equivalent with those, now so well known, in the valley of Bitter Creek, Wyoming Territory. These last-named localities were also visited at the close of the season's work, and from the strata of this horizon at Black Butt's Station three new species of Unio were obtained, making six clearly distinct species in all, that have been obtained, associated together in one stratum, at that locality. They are all of either distinctively American types or closely related to species now living in American fresh waters. They represent, by their affinities, the following living species: Unio clavus Lamarck; U. securis Lea; U. gibbosus Barnes; U. metanurus Rafinesque and U. complanatus Solander. They are associated in the same stratum with species of the genera Corbula, Corbicula, Neritina, Viparus, etc., this stratum alternating with layers containing Ostrea and Anomia.

The close affinity of these fossil Unios with species now living in the Mississippi River and its tributaries seems plainly suggestive of the fact that they represent the ancestry of the living ones. An interesting series of facts has also been collected, showing that some of the so-called American types of Unio were introduced in what is now the great Rocky Mountain region, as early as the Jurassic period, and that their differentiation had become great and clearly defined as early as late Cretaceous and early Tertiary times. Other observations suggest the probable lines of geographical distribution, during the late geological periods, of their evolutional descent, by one or more of which they have probably reached the Mississippi River system and culminated in the numerous and diverse forms that now exist there. The work of the past season shows very clearly the harmonious relations of the various groups of strata over vast areas; that although there may be a thickening or a thinning out of beds at different points they can all be correlated from the Missouri River to the Sierra Nevada Basin. The fact also that there is no physical or paleontological break in these groups over large areas from the Cretaceous to the Middle Tertiary is fully established. The transition from marine to brackish-water forms

of life commences at the close of the Cretaceous epoch and without any line of separation that can yet be detected continues on upward until only purely fresh-water forms are to be found. Dr. White, an eminent palæontologist and geologist, says that the line must be drawn somewhere between the Cretaceous and Tertiary epochs, but that it will be strictly arbitrary, as there is no well marked physical break to the summit of the Bridger Group.

THE SAND DARTER.

BY D. S. JORDAN AND H. E. COPELAND.

E have often brought home with us a "Johnny,

WE

Johnny," "Speck,”

or "Crawl-a-bottom," of a different type from any of those whose habits we already knew. It had a very sharp nose that

(FIG. 4.) THE SAND DARTER.

projected over its mouth; its body was exceedingly slim and round, as transparent as jelly, but firm and wiry to the touch. Its belly and much of its back, after a fashion peculiar to itself, were quite bare of scales, and those along the sides were small and inconspicuous. These peculiarities seemed the more striking as the other darters are scaly, and, along the middle line of the belly especially, they are often covered with hard plates, an arrangement obviously adapted to their "crawl-a-bottom " habits.

After much searching through the scattered and unsatisfactory descriptions which eastern naturalists have given us of the darters found in their bottles of alcohol, we decided that our little friend was the "pellucid darter," or better, the "sand darter" (Pleurolepis pellucidus 2 Agassiz), for reasons soon to be given.

1 American Naturalist, June, 1876. Page 335.

2 As this species is quite imperfectly known to naturalists, we here subjoin its synonymy and a description taken from the average of numerous specimens. "Etheostoma pellucidum Baird MSS., 1853."

Pleurolepis pellucidus Agassiz in Putnam's Bulletin Mus. Comp. Zoöl., 1863, 5. Cope, Cyprinidae of Penn., Supplement, 1866, 401. Le Vaillant, Recherches sur les Poissons, etc., 1874 Jordan, Indiana Geol. Survey, 1874, 214. Manual Vertebrates, 1876, 221. Jordan and Copeland, Check-List, Bull. Buffalo Soc. Nat. Hist., 1876, 135. Nelson, Bull. Ills. Mus. of Nat. Hist., Dec., 1876, p. 35. Jordan and Gilbert, Fishes of Indiana, Indiana Farmer for Jan. 17, 1877.