domes present outcrops of Morrison shale in their centers. Considerable drilling has been done in this area, and oil has been found in some wells, although the quantity appears to be small and not to offer much encouragement for profitable production. Up to 1913, however, some parts of the area had not been tested.

DEEP-SEATED STRUCTURE.

As most of the structure described in this paper is that of the Dakota and associated sandstones it is advisable to suggest that locally the same structure may not exist in the underlying formations. This difference is possible because there is an unconformity between

FIGURE 17.-Ideal section to show relations of flexures in an older formation under a monocline of younger rocks.

the Dakota and the beds below it, representing a long-time interval when the Permian and older Carboniferous strata were uplifted and their surface eroded prior to Purgatoire and Dakota deposition. This uplift was not attended by local flexing in the Black Hills, Rocky Mountain front range, southeastern Nebraska, and central Kansas, where the younger rocks lie on the older ones without noticeable discordance of attitude. If this relation prevails under the whole of the Great Plains area, which is not unlikely, the structure of the buried Permian and older Carboniferous rocks is indicated in a gen

FIGURE 18.-Syncline in older strata persisting, although considerably flattened by a flexure that developed an anticline or dome in the overlying younger rocks.

eral way by the structure lines of the Dakota sandstone. (See Pl. I.) Some possibilities of a divergent structure which might exist locally are shown in figure 17. If a district of this sort were deformed so as to develop an anticline or dome in the younger series the relations shown in figure 18 might result. Future borings in the Great Plains should be carefully watched for evidence as to the structure of the buried Carboniferous rocks. This can be done by close sampling in boring and critical consideration of the stratigraphy revealed, as compared with the succession in the areas where the rocks crop out.

OIL SHALE OF THE UINTA BASIN, NORTHEASTERN UTAH.

By DEAN E. WINCHESTER.

INTRODUCTION.

The oil shale in northeastern Utah was examined at three or four widely separated localities in 1913 with rather discouraging results.1 Two years later the study was begun in more detail by the writer near Watson,' and in view of the encouraging findings of this work a party under the direction of the writer during the field season of 1916 studied the zone of oil shale along the south side of the Uinta Basin from Watson west to Soldier Summit. This work included rough mapping of the outcrop of the rich shale zone, together with the testing of numerous samples to determine the approximate value of the shale as a future source of shale oil. In so far as they apply to that part of the Uinta Basin lying in Utah, data obtained during the previous investigations are repeated here so that the basin may be studied as a unit. The writer was assisted in the field by W. B. Wilson and John N. Massey, each of whom had participated in the work of 1915. The apparatus described in detail in Bulletin 641 was used to make the field distillations of the shale..

The reconnaissance studies of the Uinta Basin have proved the existence along its entire southern margin of a bed or beds of oil shale of minable thickness and as rich as or richer than those mined in Scotland at the present time. Previous examinations by members of the Geological Survey have revealed the fact that at practically all points along the north side of the basin, the Green River formation (containing the oil shale) is concealed beneath younger rocks which overlie the oil-shale beds unconformably, so that the area within the Uinta Basin underlain by oil shale can not be determined without extensive prospecting with the drill. However, evidence at hand seems to indicate that the oil shale may be present beneath a great part of the basin, and it is estimated that Woodruff, E. G., and Day, D. T., Oil shale of northwestern Colorado and northeastern Utah: U. S. Geol. Survey Bull. 581, pp. 1-20, 1914.

Winchester, D. E., Oil shale in northwestern Colorado and adjacent areas: U. S. Geol. Survey Bull. 641, pp. 139-198, 1916.

the Utah portion of the basin alone contains sufficient shale to produce. 42,800,000,000 barrels of crude shale oil, with perhaps 500,000,000 tons of ammonium sulphate as a by-product.

GEOGRAPHY.

The Uinta Basin is a topographic as well as a structural basin, bounded on the north by the Uinta Mountain uplift, on the south by the southward-facing Roan Cliffs, on the west by the Wasatch Mountains, and on the east by the Rangely dome and related structural features in northwestern Colorado. The oil shales of the Green River formation are exposed along the south side of the basin but are covered by younger rocks along the north side. The map (Pl. XII, in pocket) shows only an area 40 miles wide and 125 miles long on the south side of the Uinta Basin where it was possible to study the shales.

The area examined is one of extensive northward-sloping plateaus cut by many vertical-walled canyons. (See structure section on map, Pl. XII.) The Roan Cliffs, along the southern margin of the basin, south of the outcrop of the oil shale, attain at many places altitudes of more than 9,000 feet above sea level, whereas the valley of Green River, which crosses the area from north to south, is less than 5,000 feet above sea level, the maximum topographic relief of the basin thus being at least 4,000 feet. Green River, which rises far to the north in Wyoming, flows southward, crossing the area examined about 45 miles west of the east line of the State, and is joined near Ouray by White and Duchesne rivers. East of Green River the streams draining the area north of the Roan Cliffs flow northward, joining either White River or Green River; west of Green River most of the canyons lead directly to Green River in a general easterly direction. Willow, Hill, Bitter, and Evacuation creeks occupy narrow canyons in Uinta County east of Green River, and each contains water along its entire course, except Bitter Creek, which is usually dry below the mouth of Sweetwater Creek. South of Ninemile Creek Green River enters Desolation Canyon (see Pl. VI, A, p. 31) and flows in a general southward direction between nearly vertical walls which increase in height toward the south, so that in the region of the Roan Cliffs they rise 3,000 feet above the river.

The main line of the Denver & Rio Grande Railroad skirts the Roan Cliffs on the south, and although it is only a short distance from the limit of the oil-shale beds the railroad is accessible only by roundabout routes except in the western part of the field, where the shale crops out in the highlands near the track. The main line of the railroad comes within the area shown on the map west of Colton, but a branch line runs to Sunnyside, in T. 14 S., R. 14 E., and the

north end of the Uintah Railway, which connects with the Denver & Rio Grande Railroad at Mack, Colo., is at Watson, near the Colorado-Utah State line.

Wagon roads are nearly as scarce as railroads. A toll road is maintained between Watson, on the Uintah Railway, and Ouray and Vernal, in the interior of the basin, and there are two other well-kept roads connecting the interior of the basin with the Denver & Rio Grande Railroad, to the south. The one from Myton south to the head of Gate Canyon and up Ninemile Canyon to Whitmore Park and thence down Soldier Creek to Price is the older but is at present less used than the road from Duchesne southwestward up Indian Canyon and then down Willow Creek to Helper. Both routes are used by auto stages, but in 1916 the contract for carrying mail to the basin towns was in the hands of the company using the Duchesne and Helper route. During part of the year considerable travel from the interior of the basin goes westward past Strawberry Valley to Salt Lake City. However, snow prevents the use of this route in the winter season.

Except along these three principal roads the trail made by one vehicle is usually almost obliterated by wind and weather before another has cause to follow. The few ranchers who live in the valleys of Hill and Willow creeks get mail twice a week from Ouray by special messenger, usually on horseback, although there is a passable wagon road down each of these streams.

Sheep and cattle raising is the principal industry of the region, although there are small farms along the valleys of Ninemile, Argyle, Willow, and Hill creeks and also along White River near Soldier Summit. North of the area shown on the map, in the interior of the Uinta Basin, is some of the richest agricultural land of the State. The mining of gilsonite and elaterite near Watson, Fort Duchesne, Myton, and Duchesne provides employment for a considerable force of miners, and the coal mines at Sunnyside, Castlegate, and Kenilworth are points of great activity.

GEOLOGY.

PRINCIPAL FEATURES.

The field work on which the present report is based provided no opportunity for careful study of rocks other than those associated directly with the oil shale, but it was possible to make some observations of geologic phenomena in the adjacent rocks which appear worthy of record.

The Tertiary rocks that occupy the interior of the Uinta Basin have been subdivided into four formations-the Wasatch, Green River, Bridger, and Uinta―the division being based on stratigraphic and paleontologic evidence. The Wasatch, the oldest of these forma

tions, consists of coarse sandstones, highly colored shales, and conglomerates, with here and there thin lenses of coal. The Green River, which contains the oil shales, overlies the Wasatch and underlies the Bridger. It includes evenly and thinly bedded gray and white calcareous shale, with some sandstone, oolite, and limestone. The Bridger and Uinta formations comprise irregularly bedded somber-colored clay shale and ferruginous sandstone, and are distinguished from each other largely by their different fossil content, each formation being very fossiliferous.

Hydrocarbon materials have been found in all four formations, although bedded deposits (asphaltic sandstone and oil shale) are known only in the Wasatch and Green River. Veins of gilsonite, elaterite, ozokerite, and other related hydrocarbons cut all the Tertiary formations of the Uinta Basin.

WASATCH AND GREEN RIVER FORMATIONS.

The older part of the Tertiary section in the Uinta Basin is represented by a series of conglomerates, conglomeratic sandstones, shale, oolite, limestone, and oil shale, the lower part of which is undoubtedly of Wasatch age, and the upper part, containing the beds of oil shale, is of Green River age. The correlation of the middle part of this series on lithologic evidence is very difficult, especially over broad areas, inasmuch as the individual beds are not persistent and are variable in character and fossil evidence is lacking. The base of the Wasatch formation has been mapped in several areas around the margin of the basin in Colorado and Utah,' and a'zone of rich oil shale occurring in the Green River formation has been examined and mapped across the south and east sides of the basin, but the line between the two formations has never been studied. A comparison of the materials in this stratigraphic interval as exhibited in sections studied in northwestern Colorado and northeastern Utah leads to the conclusion that deposition was uninterrupted throughout the time represented by the two formations, although the conditions of deposition varied from place to place.

2

At De Beque, Colo., Woodruff 3 included in the Green River formation 1,250 feet of gray shale and sandstone below the rich oil-shale zone, and referred to the Wasatch formation more than 4,000 feet of beds, including much red and green shale, with some thin beds of coal.

1 Clark, F. R., Coal fields of the Sunnyside and Wellington quadrangles, Utah: U. S. Geol. Survey Bull. (in preparation). Hancock, E. T., Coal resources of the Meeker quadrangle, Colo.: U. S. Geol. Survey Bull. (in preparation). Gale, H. S., Coal fields of northwestern Colorado and northeastern Utah: U. S. Geol. Survey Bull. 415, 1910. Richardson, G. B., Reconnaissance of the Book Cliffs coal field, Utah: U. S. Geol. Survey Bull. 371, 1909.

2 Winchester, D. E., Oil shale in northwestern Colorado and adjacent areas: U. S. Geol. Survey Bull. 641, pp. 139-198, 1916.

3 Woodruff, E. G., Geology and petroleum resources of the De Beque oil field, Colo.: U. S. Geol. Survey Bull. 531, p. 57, 1913. Woodruff, E. G., and Day, D. T., Oil shale of northwestern Colorado and northeastern Utah: U. S. Geol. Survey Bull. 581, pp. 14, 15, 1914.