NATURE AND ORIGIN OF THE SOIL. 33 



These, then, are the three principal parts of soils sand, 

 clay, and humus, but in many cases we find them mixed 

 together or one above the other. If sand is the principal part 

 of the soil we call it a sandy soil ; if clay, a clay soil, and if 

 humus or muck, a vegetable soil. A loam soil contains a mix- 

 ture of sand and clay with some humus, and such a soil is 

 usually best fitted for growing most of the crops of the farm. 



ORIGIN OF THE SOIL. We already know where the humus 

 or vegetable matter has come from, and, as it was formerly 

 parts of plants, we conclude at once that it must contain some 

 material for feeding new plants. But where did the sand and 

 the clay come from ? 



Perhaps you have never before asked that question, thinking 

 that the clay and the sand were always in the field in that form. 

 This, however, is not the case, although they may have been there 

 for many years, perhaps for hundreds of years, perhaps for 

 thousands. Why do we say that they have not been there 

 for all time ? Well, if we go to the shore of a large lake we 

 see fresh sand being washed up day by day by the waves. If 

 we go to the banks and mouth of a large river, or even of a 

 small stream, we see sand and clay and vegetable matter being 

 washed down, carried away, and spread out to form new layers 

 of soil. If we go to the face of a high rocky cliff we can see 

 the great rocks being gradually broken down and changed 

 into piles of coarse stone, and later into finer material, and still 

 later into sand and clay. But if we can go to a range of 

 mountains or high hills we shall see more clearly the change 

 of great rocks into fine soil. 



Under our soil we find solid rock. In some places the rock 

 is at the surface, and we can see it becoming weathered and 

 rotten. The outer surface is softer than the interior. In other 

 places the rock is just under the surface. In some places we 

 have to go very deep to find the rock, but it is always there, to 

 be found if we only go deep enough. All of our sand and 



