GEOLOGY OF SOIL. 7 



an ; such are basalt, trap, and highly crystalline 

 porphyry. 



8. However named and classed are the rocks of 

 the earth's surface, they have one common origin, 

 the molten matter of the globe. Hence, having a 

 common origin, their ultimate chemical constituents 

 are similar. If granitic rocks have a certain chem- 

 ical constitution, then sandstone, slate, &c, having 

 been formed from worn out and worn down granitic 

 rocks, have a constitution chemically like them. 



9. To the agriculturist, the terms 'primary and 

 secondary, are useless. Equally so are all distinc- 

 tions of soil based on these terms. 



10. Soil is the loose material covering rocks, and 

 often is included in that term. Both are to be 

 classed by their origin. The origin of rocks refers 

 not only to the mode of their first formation, but to 

 their subsequent arrangement. The origin of all 

 rocks, geology teaches, is from the molten matter of 

 the globe. These have been, afterwards, in some 

 cases, removed by water, and in part re-modified by 

 heat [5]. Referring rocks to their origin, they are 

 divisible into two great classes. 



1st. Those formed by fire. 

 2d. Those formed by water. 



11. This division relates both to the origin and 



