CONTENTS. XV 



Phosphate of alumina and of lime 214 



JNitrate of potash and of soda. Sulphurets .... 214 



II. Organic constitxicnts of the soil. Humic acid. Geine . 215 



Crenic and apocrenic acid. Extract of humus and humin . 216 



Sect. 3. Theory of the mutual action of the organic and inorganic 

 constituents of soil, and of groimng vegetables. 



1. Action of the organic and inorganic portions of soil . . 218 



1. Of silicates. 2. Carbonates. 3. Alkalies. 4. Catalysis 219 



5. Air and water 219 



n. Mutual action of growing plants, silicates, salts, etc. . . 219 



1. General theory of the action of salts .... 220 



2. Character of the acid determines the peculiarity of effect 220 



Sect. 4. Circumstances upon which the fertility of soil depends. 



General inferences 228 



Sect. 5. Classification and description of soils. 

 Geological classification of soils. 



I. Alluvial soils. 1. Of rivers 231 



Value of alluviarsoils. 2. Peat alluvial soils . . . 232 



II. Diluvial soils. 1. Sandy and gravelly .... 233 

 2. Argillaceous, clayey and loamy 234 



III. Tertiary soils. Their origin and character . . . 2*34 



IV. Secondary soils. 1. Cretaceous or chalky soil . . 235 



2. Oolitic soil. 3. Saliferous. 4. Carboniferous. 5. Silurian 236 



V. Primary soils 237 



1. Argillaceous slate soil. 2. Limestone soil . . . 238 



3. Mica slate soil. 4. Talcose slate soil .... 239 

 5. Gneiss soil. 6. Granite soil. 7. Sienile soil . . 240 

 8. Hornblende rock soil. 9. Porphyry soil .... 241 



VI. Trappean soils. 1. Greenstone. 2. Trachyte. 3. Lava 

 soils 241 



Chemical classification of soils. 



1. Siliceous soils. Properties and mode of improvement . 243 



2. Aluminous or clay soils — their properties .... 244 



3. Calcareous soils. Properties and tests .... 246 



4. Magnesian soils ......... 247 



5. Peaty soils. Origin of. Properties, etc. . . . . 247 



6. Alluvial soils. 7. Loamy soils . . ..... 249 



