8 NATURE AND ORIGIN OF THE COIL. 



The third class soils is unusually dark in colcr from light brown 

 to dense black, such as are found in the woods where leaves and 

 branches have decayed, and in low pastures and swampy places. 

 This soil is made up of the refuse of leaves, branches and the 

 roots of plants. Sometimes we can see pieces of half-decayed or 

 rotten plants; sometimes there are very slight traces of the origi- 

 nal form of plants. This soil has, however, all come from f ormer 

 plants. We callsuch a soil a vegetable soil, and this dark colored, 

 loose material formed from the decay of vegetable matter is called 

 humus. Notice how it differs from both sand and clay. It is light 

 weight and easily worked and holds w<ater readily. 



Place a handful of swamp muck or leaf mould, humus, on an iron fire 

 shovel and carefully set it upon the burning coals. It dries out, then 

 burns away until only a small quantity of ash is left. Place some wet sand 

 on the shovel and heat, and then a little wet clay. What is the result? 



These, then, are three principle parts of soil 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 vege- 

 table soil. A loam soil contains a mixture 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 tlie humus or 

 vegetable matter has come from, and, as it was formerly parts of 

 plants, we conclude that it must contain material for feeding new 

 plants. But where did the sand and 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 hundreds of years, perhaps thousands. Why 

 do we say 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 a small stream, w 7 e see sand and clay and vege- 

 table matter washed down, carried away, and spread out to form 

 n^w layers of soil. If w T e 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 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 w T e can see it becoming withered and rotten. The 



