GENESIS OF THE SOIL AND ITS POSSIBILITIES 181 



always give some indication of the character of the 

 rocks and soils over or through which they have passed. 

 The vast quantities of mineral matters carried into 

 oceans and seas are gradually deposited as the water is 

 evaporated. If, however, these matters be very solu- 

 ble, such as common salt, sulfate of magnesia, etc., they 

 are found in concentrated solutions as is seen in sea 

 waters. In small bodies of waters, such as inland seas, 

 which have no outlet, this concentration may proceed 

 to a much greater extent than in the ocean. As an in- 

 stance of this, it may be noted that the waters of the 

 Dead Sea and Great Salt Lake are impregnated to a 

 far greater degree with soluble salts than the water of 

 the ocean. The solvent action of water on rocks is 

 greatly increased by the traces of organic (or carbonic) 

 acids which it may contain. When surface water 

 comes in contact with vegetable matter it may become 

 partially charged with the organic acids which the 

 growing vegetables may contain or decaying vegetable 

 matter produce. Such acids coming in contact with 

 limestone under pressure will set free carbon dioxid. 

 Water charged with carbon dioxid acts vigorously as 

 a solvent on limestone and some other mineral aggre- 

 gates. If such waters penetrate deeply below the sur- 

 face of the earth their activity as solvents may be 

 greatly increased by the higher temperature to which 

 they are subjected. Hence, all these forces combine to 

 disintegrate the rocks, and through such agencies vast 

 deposits of original and secondary rocks have been com- 

 pletely decomposed. The decay of nitrogenous matters 

 gives rise to nitric acid which also adds to the disinte- 

 grating power of percolating waters. The gradual 

 passing of the firm rock into an arable soil is beauti- 

 fully shown in the illustration. 



