GEOLOGY OF AGRICULTURE. 61 



practical use. Zoology has important relations to the 

 rearing of useful animals, and to the destroying of 

 noxious insects. Geology has done much to de- 

 velop resources, beneficial to all interests ; and it de- 

 serves especially well of the farmer ; it has brought to 

 light fertilizing materials of great value; and it stands 

 ready to teach various lessons, which farmers would do 

 well to hear. But of all the sciences for aiding practi- 

 cal agriculture, chemistry is first. The farmer should 

 not only heed what the cherpist tells him, but should 

 learn somethin^^ of this science for himself. It is in- 

 wrought with his very employment. The farmer's 

 whole life is spent in performing, or in aiding nature 

 to perform, chemical operations. He should under- 

 stand how the thing is done. Even when he does 

 right, without knowing why, it would at least bo a 

 satisfaction to know the reason. 



PHYSICAL CONSTITUTION OF SOILS. 



98. It has been stated, that the igneous rocks (those 

 which had their origin in the action of intense heat) 

 lie below the aqueous (those which have been deposit- 

 ed from water). This is true, with the exception of 

 such igneous rocks as have been forced up by volcanic 

 actioft through the aqueous rocks, and deposited above 

 them. Granite is the result of the most ancient vol- 

 canic action of which there is now any evidence re- 

 maining. Immense quantities of this rock seem to 

 have been forced up in a melted state, forming exten- 

 sive mountain ranges. Portions of this, as well as of 

 other rocks, have since been broken down, and scat- 



