AGRICULTURE. 471 



SOILS. 



The origin of all soils is from the decomposition of the rocks, clays, shales, 

 and other material going to make up the crust of the earth. When any part 

 of the earth's crust is exposed to the influence of the rain and dew, the cold 

 of winter and the heat of summer, no matter how compact that material may 

 be, it gradually decomposes and the particles wash down and make the soils 

 of the valley below. 



Then again the lichens, although in many instances they are of microscopic 

 size, fasten themselves upon the rocks and there secrete an acid which grad- 

 ually decomposes the rocks, and the particles go to make up the soils. The 

 clays and other soft materials are more easily broken up and washed down 

 by "the rains, and they too enter into the. composition of the soils. Again, 

 growing upon this newly made soil will be plants which in turn will die, and 

 the material of which they are composed will combine with the rock material 

 and form a soil somewhat different from that of purely mineral origin. The 

 difference in the soil is often observed in the color of the two; the last, or 

 that on top, is usually darker than that below, caused by the large amount 

 of vegetable matter contained therein. 



The material from which most soils are derived has been subjected to this 

 disintegration several times since it was first deposited as rock material. The 

 sandy soils are mostly made up from the sandstones of the different forma- 

 tions, which were in turn derived from the granites and other igneous rocks 

 and deposited along the shores of the former oceans. The calcareous soils 

 have their origin from the limestones, and the limestones were deposited in the 

 bed of the old ocean, the material coming from the worn-out shells of the by- 

 gone times. A perpetual round of disintegration, mixing, and redeposition 

 has been going on since the beginning, our soils being the work of all the 

 ages. In the classification of the soils some writers have distinguished them 

 as sedimentary soils, being those which are in the immediate vicinity of the 

 rocks from which they were formed, and the transported soils, being those 

 which have been brought from a distance. This classification will be well 

 enough if the fact be kept in mind that nearly all the stratified rock material 

 has itself been brought from another locality by the very same forces that are 

 now transporting and depositing the other class of soils. There is no rock 

 that has not at one time been soil. 



There are fifteen principal chemical properties composing all soils, aside 

 from many other elements that occur only in small quantities or not at all. 

 These are: 1, hydrogen; 2, carbon; 3, oxygen; 4, nitrogen; 5, silicon; 6, 

 chlorine; 7, phosphorus; 8, sulphur; 9, aluminum; 10, manganese; 11, 

 potassium; 12, calcium; 13, sodium; 14, magnesium; 15, iron. Besides these 



