XIV CONTENTS. 



Sect. 3. Simple jninerals which enter into the composition of the 



rocks. 



1. Quartz 183 



2. Feldspar. 3, Mica. 4. Talc 184 



5. Hornblende. 6. Serpentine. 7. Calcareous spar . . 185 

 8. Pyrites (fool's gold) .186 



Sect. 4. Composition of the rocks 



1. Igneous and aqueous rocks 187 



Igneous rocks. 1. Granite. 2. Gneiss. 3. Mica slate . . 187 



4. Argillaceous slate. 5. Talcose slate. G. Hornblende slate 188 

 7. Graywacke. 8. Trappean rocks. 9. Limestone rocks . 188 

 10. Sandstones 188 



Sect. 5. Origin of soils. 

 Agents concerned in wearing down the rocks . . . • 188 

 1. Oxygen. 2. Pyrites 189 



3. Mechanical agency of water. 4. Decaying plants . .190 



5. Growing plants 191 



Depth of soil 192 



CHAPTER V. 



SOILS, AND THEIR RELATIONS TO VEGETATION. 



Sect. 1. .Analysis of soil. 



I. Mechanical analysis and tests 195 



II. Chemical analysis of soils . . ..... 198 



Rules of analysis by Dr. Dana 198 



« " Dr. Jackson 198 



Sect. 2. Composition of soils as determined hy analysis. 



1. Mineral constituents of soil 205 



1. Earths. 



(1) Silicic acid, its quantity and of5ces .... 205 



(2) Aluminous earth, "^ " 206 



(3) Lime, « " 207 



(4) Magnesia, " '< 209 



2. .Alkalies and metallic oxides. Ammonia . . , .210 



Potassa, quantity and uses, 211 



Soda and oxide of iron, " ^ . 212 



3. Salts and urets. Common salt 213 



