MARLS. 91 



that it is useless for manufacturing purposes. It usually occurs scattered 

 through the beds in the shape of nodules, or as a cement in the sandy strata. 

 In the few places where lime has been found in quantities it is generally too 

 siliceous to be used for the manufacture of iron, though it might with great 

 advantage be burned for agricultural purposes. It is in this connection 

 that the Cretaceous inliers or limestone "islands" described on page 33 are 

 of great importance, as they are composed of very pure carbonate of lime, 

 and are the only source of such material in East Texas. They are found in 

 Anderson County, Texas, Southwestern Arkansas,* and in Louisiana, j- Prob- 

 ably a careful search will still farther prove their existence in East Texas. 

 The deposit in Anderson County is destined to be of the greatest value as a 

 flux for the iron ores of that county and the surrounding region. 



A hard bluish-gray limestone is found at Saline, in the northern part of 

 Smith County; also under similar conditions in southwestern Smith County; 

 also at the Freestone County saline, two miles east of the town of Butler. 

 Large concretionary masses of limestone, sometimes weighing over two tons, 

 are found on the Big Cypress River, near Port Caddo. These are said to 

 have been hauled to the old Kelly furnace, in Marion County, a distance of 

 twenty-two miles, as a flux. They are also said to have been taken down 

 the Big Cypress and Red rivers to Shreveport for use in paving. 



MARLS. 



The marls of East Texas are numerous, and, varying as they do in physi- 

 cal composition, differ considerably in their agricultural value. They are not 

 as rich in fertilizing ingredients as some found in other States, but they are 

 of great importance locally, inasmuch as they contain the ingredients that 

 the soils of the surrounding country most need, i. e., potash, soda, phosphoric 

 acid, lime, and magnesia. The basis of all good soil is silica or alumina, rep- 

 resented respectively by sand and clay, and associated with smaller quantities 

 of lime, magnesia, iron, manganese, phosphoric acid, potash and soda salts, 

 and ammonia in the form of decayed animal and vegetable matter, besides 

 other substances in smaller quantities. A soil composed exclusively of silica 

 or alumina, or both, would be worthless, but with the other ingredients in 

 proper proportions, they form the richest of all lands. Plants draw their 

 sustenance from three sources — the air, the rain, and the earth. From the 

 air they take carbonic acid and nitrogen (in the form of ammonia) and 

 water (in the form of a vapor). From the rain they take the carbonic acid 



* Geological Survey of Arkansas, Yol. 2, Mesozoic Geology, R. T. Hill, 1889. 

 f "Summary of Results of a late Geological Reconnoisance of Louisiana," E. W. Hilgard, 

 American Journal of Sciences and Arts, Yol. XLYIII, Nov., 1869, p. 342. 



