74 PRINCIPLES OF AGRICULTURAL CHEMISTRY 



up a large part of the deep sea deposit. Phosphoric acid is fixed 

 in small quantities in these deposits. 



Limestone deposits may be metamorphosed into limestone rock, 

 marble, or other crystalline forms of lime. By the weathering of 

 such deposits, many fertile soils have been farmed. Some old 

 soils of limestone origin are practically free of carbonate of lime, 

 and are very poor. 



Deposits in Lakes. Lakes are not permanent, geologically, but 

 are gradually filled with deposits of waste brought into them by 

 rivers, unless the lake is drained before such filling takes place. 

 The lake is first converted into a swamp, and finally into dry land. 



In lakes without an outlet, various salts are deposited. Such 

 lakes can exist only in dry climates, where the loss by evaporation 

 is equal to or greater than the amount of water brought in by 

 rivers. Rivers carry with them not only visible waste, consisting 

 of particles of rock in suspension, but also invisible waste, or 

 material in solution, which consists of carbonate of lime, sulphate 

 of lime, chloride of soda or common salt, etc. This waste 

 accumulates in lakes having no outlet. Deposits of gypsum 

 (sulphate of lime), salt, carbonate of lime, and other salts, are left 

 when such lakes dry up. The carbonate of lime is first deposited, 

 then gypsum. As the liquid becomes more concentrated, com- 

 mon salt is deposited, next sulphate of magnesia, then potash 

 salts, and chloride of magnesia. The deposition may be checked 

 by influx of water at any stage, the deposits already made being 

 perhaps covered with mud, and a new series of deposits started on 

 top of these. The German potash salts are supposed to be of 

 such origin. 



Peat and Muck Soils. When a soil is saturated with water, 

 vegetation does not decay as rapidly as in a drained soil, but 

 accumulates, forming a peat or muck soil. Peat soils are also 

 formed in cool and damp climates, by the growth of a moss, 

 which is able to hold water tenaciously. 



Soil Provinces of the United States. The Bureau of Soils 1 of 

 the U. S. Department of Agriculture divides the United States 

 1 Bulletin No. 55. 



