6 59 



from. From the trap rocks is derived a rich, fertile soil, well pro- 

 portioned in clay, sand, lime, magnesia, oxide of iron, and rich in 

 potash. With a knowledge of the rocks which went to form a soil, 

 we are in a position to say whether it is likely to be a soil that will 

 grow any particular crop. The soils derived from rocks of the 

 same age are the same in character in one part of the world as in 

 another. 



Geologists divide the rocks into two classes stratified and 

 uustratiiied. This division is quite suitable to the requirements of 

 the agriculturist. The unstratiiied rocks are called chrystalline or 

 igneous rocks, and for agricultural purposes may be divided into 

 two classes granite and trap rocks. The stratified or sedimentary 

 rocks cover the greater portion of the earth's surface, and go to 

 form the greater part of the soils. They lie over each other in hori- 

 zontal layers, like the leaves of a book when laid on its side, and 

 always in a definite position, no matter in what part of the world 

 they are found. 



Granite consists of quartz, felspar and mica in varying propor- 

 tions, and when hornblende replaces the mica it is called a syenite. 

 The fertility of a granite soil is governed by the felspar. It is 

 principally the felspar that goes to make a line soil, and its fertility 

 will greatly depend on whether the felsite is a potash or magnesia 

 felsite. Granites generally form mountain ridges. The rains wash 

 out the line felsite clay or kaolin, carrying the clay down into the 

 low flats, forming a cold, impervious, clayey soil, and leaving only 

 the barren quartz on the mountain side, more especially on the side 

 exposed to the prevailing wind and rain, while on the other side 

 may be a comparatively fertile slope, not having been denuded of 

 its line clay. It is evident that a granite soil to be fertile must lie 

 over a granite, and be derived from a granite containing a potash 

 felsite. 



The trap rocks consist of felspar, hornblende, or augite, and 

 comprise basalt and the greenstones generally. The felspar and 

 hornblende in the trap rocks are both reduced in the weathering 

 to form a soil. By a glance at the composition of these two sub- 

 stances it will be quite evident why trap rocks produce some of the 

 most fertile soils : 



