New Mexico and Utah. He was unable to pay much attention to detailed work, but had an excellent opportunity of taking a general view of the two great plain belts that liethe one along the east, the other along the west base of the Rocky Mountains. For nearly 2000 miles' travel he had constantly in view the cretaceous and tertiary formations, among which are involved some of the most interesting geological questions. He observed, among other things, the great persistency of the various groups of rocks throughout the east, west, and north, and especially, in the west, that from Northern New Mexico to Southern Wyoming the various members of the cretaceous lie in almost unbroken belts, while the tertiaries are hardly less easily followed.

Between the east and the west there is only one great incongruity. Along the east base of the mountains the upper Cretaceous rocks, including Nos. 4 and 5, are almost wanting, consisting at most of a few hundred feet of shales and laminated sandstones. Along the west base this group becomes a prominent and important topographical as well as geological feature. In the northwest, where it forms the "Mésa Verdé," and the cap of the Dolores plateau, it comprises upward of 2000 feet of coal-bearing strata, chiefly sandstone, while in the north it reaches a thickness of 3500 feet, and forms the gigantic hog-back of the Grand River Valley.

While in the south west he visited the Sierra Abajo, a small group of mountains which lie in Eastern Utah, and found, as he had previously surmised, that the structure was identical with that of the four other isolated groups that lie in the same region. A mass of trachyte has been forced up through fissures in the sedimentary rocks, and now rests chiefly upon the sandstones and shales of the lower Cretaceous. There is a considerable amount of arching of the sedimentary rocks, caused probably by the intrusion of wedgelike sheets of trachyte, while the broken edges of the beds are frequently bent abruptly up as if by the upward or lateral pressure of the rising mass. He was able to make many additional observations on the geology of the San Juan region, and secured much valuable material for the coloring of the final

map.

He states that the northern limit of the ancient cliff build

ers in Colorado and Eastern Utah is hardly above latitude 37° 45'.

The Grand River Division was directed by Mr. Henry Gannett, topographer, with Dr. A. C. Peale as geologist. Mr. James Stevenson, executive officer of the Survey, accompanied this division for the purpose of assisting in the management of the Indians, who last year prevented the completion of the work in this locality by their hostility.

The greater portion of the work of this division lay north of the Grand River, limited on the north by the parallel of 39° 30', and included between the meridians of 108° and 109° 30'.

This division took the field at Cañon City, Colorado, about the middle of August. The party traveled nearly west, up the Arkansas River, over Marshall's Pass, and down the Tomichi and Gunnison Rivers to the Uncompahgre (Ute) Indian Agency. Here they secured the services of several Indians as escort in the somewhat dangerous country which they were first to survey. This area lying south of the Sierra La Sal was worked without difficulty. It is a broken plateau country, and presents many curious pieces of topography. Eleven days were occupied in this work.

The Grand River, from the mouth of the Gunnison to that of the Dolores, i. e., for nearly a hundred miles, flows along the southern edge of a broad valley, much of the way being in a low cañon, one hundred to two hundred feet deep. The course of the river is first northwest for twenty-five miles, then, turning abruptly, it flows southwest, and then south for about seventy-five miles. This valley has an average width of twelve miles. It is limited on the north and west by the Roan, or Book Cliffs, and their foot-hills, which follow the general course of the river. These cliffs rise from the valley in a succession of steps to a height of about 4000 feet above it, or 8000 to 8500 above the sea.

From its crest, this plateau (for the Book Cliffs are but the southern escarpment of a plateau) slopes to the N.N.E. at an angle of not more than 5°. It extends from the Wahsatch Mountains on the west to the foot-hills of the Park Range on the east, and presents every where the same characteristics. The Green River crosses it, flowing in a direction exactly the reverse of the dip. It borders the Grand on the north for

one hundred and fifty miles, the east forming the divide between the Grand and the White. On the south side of the crest are broken cliffs; on the north side, the branches of the White cañon immediately. This leaves the divide in many places very narrow, in some cases not more than thirty to forty feet wide, with a vertical descent on the south toward the Grand River, and an extremely steep earth slope (35° in many cases) at the heads of the streams flowing north to the White River. This crest, though not over 8500 feet in height, is the highest land for a long distance in every direction.

After leaving the Uncompahgre Agency, the party followed Gunnison's Salt Lake road to the Grand, and down that river to the mouth of the Dolores, in latitude 38° 50', longitude 109° 17'. At this point they turned northward, and went up to the crest of the Book Plateau. They followed this crest to the eastward for upward of a hundred miles to longitude 108° 15', and thence via the White River (Ute) Indian Agency to Rawlins, where they arrived on October 23d.

The whole area worked is about 3500 square miles, in surveying which about sixty stations were made.

The geological work of this division, by Dr. Peale, connects directly with that done by him in 1874 and 1875. Sedimentary formations prevail on both districts visited the past

season.

The country first examined lies between the San Miguel and Dolores Rivers, extending northward and northwestward from Lone Cone Mountain. The general character of this region is that of a plateau cut by deep gorges or cañons, some of which, especially toward the north, extend from the sandstones of the Dakota group to the top of the red beds. The depth of the cañon, however, is no indication of its importance as a stream-bed, for away from the main streams they are dry the greater portion of the year. There are not great disturbances of the strata, what folds do occur being broad and comparatively gentle.

The San Miguel River, leaving the San Juan Mountains, flows toward the northwest, and with its tributaries cuts through the sandstones of the Dakota group, exposing the variegated beds lying beneath, that have generally been referred to the Jurassic. About 25 or 30 miles north of Lone Cone the river turns abruptly toward the west, and flows

west and southwest for about 15 miles, when it again turns, and flows generally northwest until it joins the Dolores. Between the San Miguel and Lone Cone, the sandstones of the Dakota group (or No. 1 cretaceous) are nearly horizontal, forming a plateau which, on approaching the mountains, has a capping of cretaceous shales.

Beyond the bend, the San Miguel flows in a monoclinal. valley, in which the cañon walls are of the same description as in the upper part of its course. As the mouth is approached the red beds appear. Between this portion of the course of the San Miguel and the almost parallel course of the Dolores, which is in a similar monoclinal rift, there are two anticlinal and two synclinal valleys parallel to each other. They are all occupied by branches of the Dolores. Lower Cretaceous, Jurassic, and Triassic strata outcrop, and present some interesting geological details, which will be fully considered in the report on the district. The Dolores River comes from a high plateau in a zigzag course, flowing sometimes with the strike and sometimes with the dip of the strata. Its general course on the western line is about northwest, from which it turns to the northward and westward, finally changing to northwest again to its junction with the Grand. It is in cañon the greater part of its course. In the region of country north of Grand River the geological formations extend uninterruptedly from the red beds exposed on Grand River to the white tertiary cliffs forming the summit of the "Roan Mountains," or Book Cliffs. The Grand is generally in a cañon in the red beds.

On the north side the No. 1 cretaceous sandstone forms a hog-back sloping toward the cliffs. Between the crest of this hog-back and the cliffs there is a broad valley formed by the erosion of the soft cretaceous shales which extend to the base of the cliffs, and in some places form their lower portion. The cliffs are composed mainly of cretaceous beds, rising one above another in steps, until an elevation of about 8000 feet is reached. The summit is the edge of a plateau sloping N.N.E. This plateau is cut by the drainage flowing into the White River from the south. These streams rarely cut through the tertiary series.

Coal of poor quality is found in the sandstones of the Dakota group, and also in the sandstones above the middle

cretaceous beds. Wherever noticed, it was in thin seams and of little economic importance.

The White River Division was directed by G. B. Chittenden as topographer, accompanied by F. M. Endlich as geologist.

The district assigned to this party as their field for exploration during the season of 1876 commenced from the eastward at longitude 107° 30', joining on to the work previously done, and extended westward 30 miles into Utah Territory. Its southern boundary was north latitude 39° 30', while the White River formed the northern limit. In order to take the greatest possible advantage of the short time that could be allowed, it was determined to make the White River Agency the head-quarters, and in two trips from there complete the work. About 3800 square miles comprised the area surveyed.

In working up the topography of the district, the party spent 48 days of absolute field - work, made 41 main topographical stations and 16 auxiliary ones, and traveled within the district about 1000 miles. The party ascertained the course of all the main trails, the location and quality of nearly all the water-which is scanty throughout-and can map with considerable accuracy the topographical forms and all the water-courses. The area is almost entirely devoid of topographical "points," and the topographer is obliged to depend to a considerable degree on those far to the north and south for the triangulation. The country has been heretofore almost entirely unexplored, and was described by the nearest settlers as a broken cañon country, extremely dry. It was marked on the maps as a high undulating plateau, with fresh-water lakes and timber. The party saw no lakes of more than four hundred yards in diameter, and only two or three of those. The country is nearly all inhabitable both winter and summer, and considerable portions of it valuable, and, though three quarters of it is within the Ute Indian Reservation, the advantage of a more accurate knowledge of its character can readily be seen.

Altitudes were determined by the mercurial barometer, with a base at the White River Indian Agency, and checked by a continuous system of vertical angles. The altitude of the Agency has been determined by a series of barometric