The area is not densely populated; though all parts of it are inhabited. The rural population is sparse except in the level or gently rolling upland and valley areas where tillable land occurs in greatest amounts. The largest town is De Queen, the county seat of Sevier County. Among the other important towns are Murfreesboro, the county seat of Pike County; Dierks, Center Point, Highland, and Delight. All these towns except Center Point are on railroads.

The main line of the Kansas City Southern Railway runs northward through De Queen. The De Queen & Eastern Railroad extends eastward from De Queen as far as Dierks, though a few miles of its track lies south of the area shown on Plate I. The Prescott & Northwestern Railroad enters the area at Tokio and extends as far as Highland. The Memphis, Dallas & Gulf Railroad also enters the area at Tokio and passes northeastward through Murfreesboro to the east border. A branch of the St. Louis, Iron Mountain & Southern Railway enters the area and extends to the northwest as far as Pike. Public and secondary roads reach all parts of the area, but only a few are maintained in good condition. On account of the character of the topography not many of the roads follow section lines.

GEOLOGY.

GENERAL FEATURES.

The rocks of the area shown on the map (Pl. I) and of adjoining parts of the Gulf Coastal Plain and the Ouachita Mountain region are all of sedimentary origin except four bodies of diamond-bearing peridotite near Murfreesboro. Those in the Ouachita region are of Paleozoic and Quaternary age. The Paleozoic rocks, which range from Cambrian to Carboniferous, consist mainly of shale, sandstone, novaculite, and chert and have an aggregate thickness of 26,000 feet in west-central Arkansas. They have been subjected to intense folding, so that the beds stand at high angles. the folds have an eastward trend. The rocks along the northern border of the area here described are shales and sandstones of Car

boniferous age.

Most of

In that part of the area stream gravels and silts of

Quaternary age occur only as narrow strips or small patches along

Some of the streams.

The sedimentary rocks of the Coastal Plain portion of the area are of Lower Cretaceous, Upper Cretaceous, and Quaternary age. The Lower Cretaceous series is represented by the Trinity formation, the Cpper Cretaceous series by the Bingen and Brownstown formations, and the Quaternary system by extensive terrace and alluvial deposits. The Trinity and Bingen formations and the terrace and alluvial deposits contain the gravels here described.

The gravels and their residual materials consist mainly of novaculite pebbles and are very similar in lithologic character. Their abundance and resistance to weathering make them the predominating surficial deposits in the area. Because of disturbance by creep, landslides, and redeposition and because of the great number of beds, it is difficult at many places to follow them across the country and to determine whether or not they are in their original place of deposition. As they have yielded no fossils, their age has been determined by their stratigraphic relations to adjacent beds.

TRINITY FORMATION.

The Trinity formation is exposed in a belt extending from east to west across the area shown in Plate I. This belt has irregular north and south borders, is narrowest to the east, and is continuous except where the formation is covered by surficial deposits of alluvium and terrace remnants along the southward-flowing streams and their tributaries.

The character of the formation is graphically represented in figure 6. It consists of clay, sand, gravel, limestone, gypsum, and celestite, named in the descending order of abundance. The limestone occurs in two beds. The older one is here named the Dierks limestone lentil, and the younger the De Queen limestone member, from the towns at and near which they are exposed. The gravel also occurs as two beds, one at the base of the formation, here named the Pike gravel member, from the village of Pike, and one younger than the Dierks limestone, here named the Ultima Thule gravel lentil, from the village of Ultima Thule.

The Trinity and overlying Cretaceous strata have a low southward dip, as explained in the next paragraph, but they rest upon the peneplaned edges of highly tilted Carboniferous strata. A pronounced unconformity, therefore, occurs at the base of the Trinity. A notable though less striking unconformity exists between the Trinity and the Bingen formation, of Upper Cretaceous age. This unconformity is shown by the eastward truncation of the beds of the Trinity and the resulting overlap of the Bingen.

The formation ranges in thickness from about 70 feet north of Delight to over 600 feet, indicated by a well 2 miles north of Center Point, which reached a depth of 500 feet without striking bedrock. The southward dip of the strata and also of the Cretaceous floor, as determined from the different elevations of the Pike gravel member along its outcrop, averages about 80 feet to the mile, being in few places less than 60 feet or more than 100 feet to the mile. But according to the well just mentioned the dip increases toward the south and is over 100 feet to the mile near Center Point. A similar southward dip exceeding 100 feet to the mile near De Queen is indi

Gray cross-bedded sand in heavy beds; some clay.

(Irregularly bedded pebbles and cobbles as much as 10 inches in diameter.

FIGURE 6.-Generalized section of Cretaceous rocks exposed in the Caddo Gap and De Queen quadrangles,

Arkansas and Oklahoma.

cated by the ice-factory well at that place, which was put down to a depth of 249 feet without reaching Carboniferous rocks. As a result of this southward dip the beds are exposed in east-west belts in which the younger rocks lie to the south and the older ones to the north.

The Pike gravel member is the thickest and most persistent gravel bed in the area, and has a larger surface distribution than any other. In much of its belt of outcrop it forms an even though dissected southward-dipping upland. This form is due to the resistant nature of the gravel and the ease with which the overlying unconsolidated clay and sand have been eroded. Some of the larger areas of outcrop are at or near Pike, Nathan, Muddy Fork, Dierks, Lebanon, and King. The thickness is rather uniform, being in most places between 20 and 50 feet, but it apparently attains 100 feet near Pike. The gravel thins out at a few places, as near Murfreesboro and Lebanon, where rocky headlands and islands of Carboniferous sandstone along the old Cretaceous shore were not completely buried by the gravel, though they were by higher beds. The sand and clay separating the Ultima Thule and Pike gravels thin to the west and are absent just west of the State line, in consequence of which the Ultima Thule gravel rests either upon the Pike gravel or upon Carboniferous rocks. If the Pike gravel is present there it can not be distinguished from the overlying gravel.

This gravel consists of pebbles usually less than half an inch in diameter, but it contains many larger ones and also many cobbles as much as 10 inches in diameter. These larger pebbles and cobbles are at most places especially abundant in a thickness of several feet at the base. The pebbles and cobbles are partly to thoroughly rounded. Most of them are dense white, gray, brown, black, or red novaculite, unquestionably derived from the Arkansas novaculite, which is exposed in the Ouachita Mountains north of the area here described. A small number, however, are quartz, quartzite, and sandstone. Those of quartzite and sandstone are most abundant in the cobble bed, but they constitute a minor portion of it. The proportion of quartz pebbles in the Pike gravel and the Ultima Thule gravel increases westward from the longitude of De Queen. They are derived from quartz veins in McCurtain County, Okla., which are largest and most numerous in the Ordovician shales in the central part of the county. The proportion of pebbles derived from the novaculite in that county likewise increases westward from the longitude of De Queen. Some of the gravel is conspicuously cross-bedded. Most of it is loose and contains some sand or clay as lenses in the upper part and as a filling in the interstices between the pebbles. Nearly horizontal beds of gravel are in places cemented by brown