64 GEOLOGY OF AGRICULTUEE. 



pebbles, and coarse gravel) — if, with regard to these, 

 he finds the original locality from one to five hundred 

 miles distant, all of which is sustained by the very 

 best authorities, no one, that I know, disputing — it 

 follows, of course, that soils depend very little, for 

 their composition and capabilities, upon the rocks im- 

 mediately underlaying them. This view is confirmed 

 by analyses of soils. * No more carbonate of lime, for 

 instance, is found in lime-stone regions than in others. 

 The same is true of other ingredients of soils. They 

 are not always found in soils overlaying the rocks that 

 contain them. ] Soils do not come from the underlay- 

 ing rock, but from wide-spread regions, generally north 

 and north-west of their present location. Hence, if 

 rocks were ever so varied in their constitution, it would 

 not follow that soils are. | 



ROCKS AND MINERALS. 



85. The truth is, that rocks themselves are not as 

 various in composition as many suppose. " Seven or 

 eight simple minerals constitute the great mass of all 

 known rocks. These are — 1, quartz ; 2, felspar ; 3, 

 mica ; 4, hornblende and augite ; 5, carbonate of lime ; 

 6, talc, embracing chlorite and soap-stone ; 7, serpen- 

 tine. Oxide of iron is also very common, but does 

 not usually show itself till the decomposition of the 

 rock commences." — Hitchcoch^s Geol.^ p. 45. 



86. From the same high authority we learn that 

 " The following constitute nearly all the binary com- 

 pounds of the accessible parts of the globe : 1, silica ; 



