15 



phere, combining with certain ingredients of the rocks. Thus 

 those rocks which contain lime and alkalies, are acted upon by 

 the carbonic acid of the atmosphere. Those containing iron by 

 the oxygen. These actions of the atmosphere are also assisted 

 by the root-growth of plants, by the burrowing of worms and 

 other underground creatures, and also in no small degree by 

 the acids (humic, geic, crenic,) generated by the decay of or- 

 ganic substances. 



The rocks essential to the formation of fertile soils, and from 

 which they are usually formed, are Granite, Feldspar, Lime- 

 stone, Gypsum, Phosphorite, Slate and Sandstone. 



Granite derives its name from its granular structure, and 

 is composed of a mixture of grains of Mica, Feldspar, and 

 Quartz. 



Quartz forms the transparent grains, and is composed simply 

 of silica. 



Feldspar, the dull creamy opaque grains, is composed of silica, 

 alumina, potash, soda, and lime. 



Mica, so called, from its forming the glittering scales, is a com- 

 pound of silica, alumina, and potash ; in some varieties the 

 alumina is replaced by iron, and the potash by magnesia. 



Limestone is a compound of lime and carbonic acid, and is 

 formed of the remains of shell fish and coral insects. The 

 lime of the soil is derived from limestone, gypsum and phos- 

 phate of lime. Gypsum is a compound of lime and sulphuric 

 acid, and is found in some places in vast beds, while the phos- 

 phate of lime (phosphorite) is more rare. In Canada and 

 .Northern New York it occurs in the ancient unstratified rocks 

 as the apatites ; in South Carolina also it i* found in the recently 

 discovered phosphate beds, which are, perhaps, the largest and 

 most available sources of phosphoric acid in the world. 



The country is indebted to Dr. N. A. Pratt, of Chaleston, for 

 discovering the value, and aiding in the development of this 

 great source of national wealth. He says, in his report on this 

 subject: "This bed has long been known in the history of the 

 geology of South Carolina, as the "Fish bed of the Charleston 

 Basin," on account of the abundant remains of marine animals 

 found in it Professor Holmes, of Charleston, having not less 

 than 60,000 sharks' teeth alone, some of them of enormous 

 size, weighing from two to two and a half pounds each. The 

 bed outcrops on the banks of the Ashley, Cooper, Stono, Edisto, 

 Ashepoo, and Combahee rivers; but is developed most richly 

 and heavily on the former, and has been found inland forty or 

 fifty miles. Near the Ashley river, it paves the public high- 

 ways for miles ; it seriousty impedes and obstructs the cultiva- 

 tion of the land, affording scarcely soil enough to hill up the 

 cotton rows ; and the phosphates have for years past been 

 thrown into piles on the lawns and into the causeways over 

 ravines, to get them out of the reach of the plows. It under- 



