64 MINERAL RESOURCES OF ALABAMA. 



underlying Tertiary formations, there are pyritous earths which 

 have been put to commercial use in Choctaw, Washington, 

 Clarke, Escambia, and other counties by leaching out the sul- 

 phates of iron and alumina and putting them on the market as 

 "mineral extract," "acid iron earth/' etc. , 



At Greenville, in Butler county, a strong' solution of these 

 acid sulphates is obtained from a shallow well, and is well 

 known over the state as a medicinal agent. 



Nitre. 



The limestone caves of the northern part of the state con- 

 tain large quantities of nitre, which during the civil war was 

 obtained from this source for the manufacture of gunpowder. 

 The marks of the picks then used are still to be seen plainly at 

 some of the localities. 



Although an organic substance, the bat guano, so abundant in 

 many of the caves referred to, may be mentioned in this con- 

 nection. This fertilizer contains 25 per cent, of organic mat- 

 ter, 6 per cent, of nitrogen, mainly in the form of uric acid, and 

 from i to 3 per cent, of phosphoric acid, I to 3 per cent, of pot- 

 ash, and .6 per cent, of ammonia. 



Phosphates. . 



Silurian Formation. The phosphates of the Mount Pleasant, 

 Tenn., district extend down into Alabama for two or three miles 

 along Elk River and its western tributaries, Sugar Creek and 

 Little Shoal Creek, into Limestone county. They also show 

 along the state line for several miles to the east of Elk river, 

 extending in places a quarter of a mile or more into Alabama. 

 The geological horizon is probably Trenton, as in Tennessee. 

 The phosphatic rocks do not outcrop over much area since they 

 are usually in comparatively narrow valleys far below the gen- 

 eral level of the country, but they underlie some large level 

 tracts and second bottoms of the river and creeks, and are seen 

 also covering hillsidies. Exposures of more than TOO acres of 

 these rocks occur along the line of the L. & N. railroad about a 

 mile south of the state line. 



