gas have been produced from the South El Dorado field, the East El Dorado field, the Stephens field, and the Irma field. At present, however, the commercial gas supply of southern Arkansas comes from the eastern portion of the Smackover field from what is known as the "2,700-foot sand," which is usually found about 100 feet below the top of the so-called Blossom sand. The rock pressure on closed wells is now (December, 1926) from 450 to 600 pounds per square inch. About sixty-nine wells are producing at the present time. The production of this field is now about 100,000,000 cubic feet per day. The Natural Gas & Fuel Company of El Dorado sells about 60,000,000 cubic feet per day to refineries and industrial users. The city of El Dorado uses about 35,000,000 cubic feet per day, and the field users burn about 10,000,000 cubic feet per day.

The following are three analyses from the southern field, according to the U. S. Bureau of Mines:

1.

2.

*Value at point of consumption.

Bibliography of Gas in Arkansas

1910

Harris, Gilbert, "Oil and Gas in Louisiana, With a Brief Summary of Their Occurrence in Adjacent States."-U. S. Geological Survey, Bulletin No. 429. Out of print, but may be consulted in public or scientific libraries.

1912

Smith, Carl D., "Structure of the Fort Smith-Poteau Gas Field, Arkansas and Oklahoma."-U. S. Geological Survey, Bulletin No. 541b, pp. 23-33. Out of print, but may be consulted in public or scientific libraries.

3.

4.

5.

6.

7.

8.

9.

1920

Branner, J. C., "Oil and Gas Geology," in "Outline of Arkansas Geology," by J. G. Ferguson. Obtainable from Commissioner of Mines, Manufactures, and Agriculture, State Capitol Bldg., Little Rock, Ark.

1921

Pratt, Wallace E., "The Recent Discovery of Oil and Gas at El Dorado, Arkansas."-Bulletin of the American Association of Petroleum Geologists, Vol. 5, pp. 90-91. Obtainable from American Association of Petroleum Geologists, Business Manager, Box 1852, Tulsa, Okla.

1922

Bell, H. W., and Kerr, J. B., "The El Dorado Oil and Gas Fields." Published jointly by the U. S. Bureau of Mines and the Arkansas State Bureau of Mines. Out of print, but may be consulted in public or scientific libraries.

Drake, N. F., "Petroleum and Natural Gas in Arkansas," in "Minerals of Arkansas," by J. G. Ferguson. Obtainable from Bureau of Mines, Manufactures, and Agriculture, State Capitol Bldg., Little Rock, Ark.

1923

Haury, P. S., Bell, H. W., and Kelly, R. B., "The Preliminary Report on the Eastern Part of the Smackover, Arkansas, Oil and Gas Fields."Published jointly by the U. S. Bureau of Mines and the Arkansas Bureau of Mines. Out of print, but may be consulted in public libraries.

Wilson, Malcolm E., "Oil and Gas Developments in Northern Loui siana and Southern Arkansas in 1923."-Paper 1335P of the American Institute of Mining and Metallurgical Engineers, 29 W. 30th Street, New York. Obtainable from same address.

1924

Engineering Report on the Smackover Oil and Gas Fields, Ouachita and Union Counties, Arkansas.”—Published jointly by the U. S. Bureau of Mines and Chamber of Commerce, El Dorado. Price, $1.00. Obtainable from El Dorado Chamber of Commerce, El Dorado, Ark. For further references see Petroleum Bibliography.

ONYX MARBLE

Onyx is properly a banded variety of chalcedony, a form of silica. Onyx marble or Mexican onyx are popular names for a banded variety of either calcite or aragonite or stalagmitic marble. Such marble which is translucent, takes a brilliant polish and is sometimes beautifully mottled or banded.

Composition. Onyx marble crystallizes as one of two distinct mineral formations, calcite or aragonite. Of these, aragonite is the rarer and harder and takes a more brilliant polish.

Uses. Onyx marble is used as an interior decorative stone, for statuettes, lamp shades or bases, etc.

Occurrence. So far as is known, all of the onyx marble of any value in Arkansas occurs in rocks of Ordovician age. Some of the cave deposits in these rocks near Eureka Springs furnish a fairly good grade of onyx marble. Some of the material is translucent and brightly banded. It works easily and takes a brilliant polish. A deposit occurs in Section 14, Township 20 north, Range 17 west, where it is found in white, cream, red, and yellowish brown colors. Slabs four or five feet square could be obtained from Dirst's cave in the same section. Slabs containing several square feet of onyx marble have been quarried near Eureka Springs and made into paper weights, souvenirs, etc. Samples of onyx marble have been sent in to the Geological Department from Sharp County, from the southern part of Baxter County, from Marion County, northwest of Oakland on Water Creek in Marion County, and on Livingstone and North Sylamore Creeks. It is quite possible that a systematic search for onyx marble in caves through the Ordovician region of north Arkansas would result in the discovery of workable deposits of onyx marble.

1.

Bibliography of Onyx Marbles

1890

Hopkins, T. C., "Marbles and Other Limestones."-Annual Report of the Arkansas Geological Survey for 1890, Vol. IV. Now out of print, but may be consulted in public or scientific libraries.

PORTLAND CEMENT MATERIALS

Portland cement is the most important hydraulic cement in the United States today. The use of this material has developed to such an extent that the total production of Portland cement is exceeded in value by only a few other manufactured products. The industry stands third as a consumer of coal. The manufacturing of Portland cement is not centralized, as is the case of steel manufacturing and other industries, but is distributed throughout the country on the basis of the availability of limestones and clays, cheap fuel, transportation, and markets. There are approximately 130 cement plants in operation in this country today.

Portland cement is obtained by burning to the point of fusion, a mixture of limestone and clay which contains definite proportions of lime, silica, alumina, and iron-oxides. The clinkers formed by this fusion are finely ground and the powdered material is marketed. In the burning of the raw material, calcium silicates and a calcium. aluminate are formed. Reduction of the clinker to powder allows a speedy and intimate mixture with water, which is necessary, for the setting properties of the cement depend upon a reaction which will only take place in the presence of water.

When Portland cement "sets," the compounds which were formed by burning, liberate gelatinous silica and aluminate when mixed with water. The hardening of these gelatinous materials binds the filling material and renders the cement hard and strong. As the success of this cement is therefore dependent upon the formation of definite chemical compounds, it is clear that the materials utilized in its manufacture must conform in composition to definite chemical analyses.

The raw materials for manufacture of Portland cement should contain about 75% calcium carbonate or lime, and the balance clay. Not more than 5% or 6% of magnesium carbonate should be present, and alkalies and sulphates should not exceed 3%. Chert, flint, or sand in any amount are undesirable. The ratio of Al2O3 to SiO: should be about 1:3.

The following analyses are taken from the U. S. Geological Survey Mineral Resources for 1907.