Saline County, Tertiary clays used for jugs, crocks, jars, art pottery, and other clay ware at Benton; burns solid cream color.

Sebastian County, pottery clays have been located in Sebastian County near the north base of White Oak Ridge. They are formed by the decomposition of the shales in that region. These clays are only available for rough pottery.

Union County, considerable quantities of pottery clay exist in Union County. The Tertiary clays are widely distributed and are best exposed along creek banks and ravines. The clays of this county have not been mapped.

Yell County, Carboniferous shale formerly used in the southeast quarter of Section 12, Township 6 north, Range 21 west. Rough pottery has been made from the Pennsylvanian clay in the vicinity of Dardanelle. Such clay would probably not be suitable for the manufacture of fine pottery.

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Bibliography of Clays of Arkansas

1891

Eakins, L. G., “Analysis of Kaolin from Garland County, Arkansas." -U. S. Geological Survey Bulletin No. 78, pp. 12-13. Out of print, but may be consulted in public libraries.

1906

Eckel, Edwin C., "The Clays of Garland County, Arkansas."-U. S. Geological Survey, Bulletin No. 285, 1908. Now out of print, but may be consulted in public libraries.

1908

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Branner, J. C., "The Clays of Arkansas."-U. S. Geological Survey, Bulletin No. 351, 1908. Now out of print, but may be consulted in public libraries.

1915

Steiger, George, "Analyses of Clays from the Hot Springs District, Arkansas."-U. S. Geological Survey, Bulletin 591; also Bulletin No. 419. Both may be obtained from the U. S. Geological Survey, Washington, D. C., 591 for 40c and No. 419 for 25c.

1922

Ries, Herwich, "High Grade Clays of the Eastern United States," with notes on some western clays.-U. S. Geological Survey, Bulletin No. 708. Obtainable from the U. S. Geological Survey, Washington, D. C., for 60c.

1926

Branner, Geo. C., “Abundant Variety of Clays in Arkansas, with Gas, Oil and Coal Available."-January 28, 1926, issue of Manufacturers' Record. Obtainable from Manufacturers Record, Baltimore, Md.; single copy, 20c.

COAL (Including Lignite)

The Arkansas coal fields are made up of the bituminous and semi-anthracite fields of the western Arkansas River Valley and of the lignite areas of the southern Coastal Plain. The lignites of southern Arkansas have, up to the present time, been developed only to a small extent and will be discussed later.

The western Arkansas coal was formed during the early Pennsylvanian portion of the Carboniferous era from vegetable matter which grew in the dense swamps of that time. This vegetable matter fell into water and was preserved from decay and eventually changed to peat. This was covered by some impervious material,

probably mud or clay, and the land slowly submerged until the original bed was deeply buried. While covered this way the peat probably changed to lignite and eventually into harder coal while the sands and clays which covered it slowly changed into sandstones and shales.

The coal lands of western Arkansas are concentrated in a rather narrow belt along the western end of the regional syncline between the Ozark and Ouachita Mountain regions. The Arkansas field is an eastern extension of the Oklahoma field with which it is usually designated as a portion of the western interior coal field of the United States. The productive coal measure beds are distributed principally

along the major synclinal trough which extends eastward from Fort Smith through Crawford, Sebastian, Franklin, Johnson, and Logan counties to the vicinity of Russellville, Pope county, a distance of about seventy-five miles. This area is about twenty miles wide and decreases in width toward the eastern end. The remainder of the developed coal field extends south of Fort Smith into southern Sebastian and northern Scott counties. In addition, coal is found in other relatively small areas in the Arkansas River Valley region north of the Ouachita Mountains. These areas are, however, usually widely separated and occupy the topographically prominent points of the Arkansas Valley, such as Magazine Mountain, Petit Jean Mountain, and Mount Nebo, and do not constitute any important part of the coal lands of the State.

The area of workable coal lands within the State is estimated at between 300 and 350 square miles and the total area covered by coal measure beds at about 1,620 square miles.

General Geology

The coal-bearing formations of Arkansas are confined to the lower part of the Pennsylvanian series of beds which in Oklahoma is usually classified as the McAlester shale. This formation has, in Arkansas, been divided* into the Spadra shale, the Fort Smith formation, and the Paris shale. These three formations make up a total thickness of about 1,700 feet and are underlaid by the Pennsylvanian Hartshorne sandstone and Atoka shale which together have a thickness varying from 1,800 to 6,000 feet or more. The Atoka shale car

ries some coal, but the seams are usually only a few inches thick and coal mined from them is consumed locally.

*Coal-Bearing Rocks of Arkansas

As in Oklahoma, by far the larger coal production of Arkansas has come from the top of the Hartshorne sandstone and is known as Hartshorne coal. This probably makes up 99 per cent of the Arkansas output. The upper portion of the Fort Smith formation has been mined for coal near Charleston, Franklin county, and produces "Charleston" coal, and the middle of the Paris formation is mined near Paris, Logan county, and produces "Paris" coal.

*U. S. Geological Survey Bulletin 326, "The Arkansas Coal Field," by A. J. Collier.

The coal measure beds are made up of sandstones and carbonaceous shales, the shales predominating by a large margin. Limestones, dolomites and hard calcareous beds are conspicuously absent.

The structural conditions found in the coal fields are very largely responsible for the distribution of the coal and the economic importance of the beds. The formations making up the Arkansas River Valley, occupying as they do the lowest portion of the regional syncline, have been considerably folded, twenty-three major anticlines having been mapped in the coal-bearing area. This folding is reflected in the topography of the region by numerous east-west ridges which usually rise about 75 or 100 feet above the valley floor. Many of these are twenty miles or more in length. Many of these folds have been eroded and faulted and this condition has not infrequently been the cause of the termination, discontinuity, and thinning out of the seams and has been a contributing factor to the cost of mining. These features have also been largely responsible for the division of the field into a series of separated mining districts.

The coal increases in hardness in a fairly consistent manner from the western Arkansas line eastward, and contains about three to six times as much fixed carbon as volatile combustible matter in the western portion and from seven to nine times as much in the eastern. It thus grades from bituminous through semi-bituminous to a semianthracite. About 15 per cent of the coal produced is semi-anthracite. The following table shows the increase in the ratio of the fixed carbon to the volatile combustible matter in the coal from the west end of the field to the east.

One of the most commonly used classifications of coal is that proposed by P. Frazer, Jr. This is based on the relation between the amount of fixed carbon and the volatile combustible matter (fuel ratio) in the coal, and is given as follows: