tailieunhanh - THE SOILORIGIN OF THE SOIL

The word soil occurs many times in this little book. In agriculture this word is used to describe the thin layer of surface earth that, like some great blanket, is tucked around the wrinkled and age-beaten form of our globe. The harder and colder earth under this surface layer is called the subsoil. It should be noted, however, that in waterless and sun-dried regions there seems little difference between the soil and the subsoil. Plants, insects, birds, beasts, men,—all alike are fed on what grows in this thin layer of soil. If some wild flood in sudden wrath could. | THE SOIL ORIGIN OF THE SOIL The word soil occurs many times in this little book. In agriculture this word is used to describe the thin layer of surface earth that like some great blanket is tucked around the wrinkled and age-beaten form of our globe. The harder and colder earth under this surface layer is called the subsoil. It should be noted however that in waterless and sun-dried regions there seems little difference between the soil and the subsoil. Plants insects birds beasts men all alike are fed on what grows in this thin layer of soil. If some wild flood in sudden wrath could sweep into the ocean this earth-wrapping soil food would soon become as scarce as it was in Samaria when mothers ate their sons. The face of the earth as we now see it daintily robed in grass or uplifting waving acres of corn or even naked water-scarred and disfigured by man s neglect is very different from what it was in its earliest days. How was it then How was the soil formed Learned men think that at first the surface of the earth was solid rock. How was this rock changed into workable soil Occasionally a curious boy picks up a rotten stone squeezes it and finds his hands filled with dirt or soil. Now Pg 2 just as the boy crumbled with his fingers this single stone the great forces of nature with boundless patience crumbled or as it is called disintegrated the early rock mass. The simple but giant-strong agents that beat the rocks into powder with a clublike force a millionfold more powerful than the club force of Hercules were chiefly 1 heat and cold 2 water frost and ice 3 a very low form of vegetable life and 4 tiny animals if such minute bodies can be called animals. In some cases these forces acted singly in others all acted together to rend and crumble the unbroken stretch of rock. Let us glance at some of the methods used by these skilled soilmakers. Heat and cold are working partners. You already know that most hot bodies shrink or contract on cooling. The early rocks were