590 MANUAL OF NATURAL HISTORY. 



ing these coral-masses, and depositing it in a new 

 form. 



IT. Group. — Soil Deposits. 



The uppermost stratum of the earth's crust is 

 formed of soil, produced by organic agency, and con- 

 sists of decomposed animal and vegetable substances, 

 with an earthy admixture. 



Inorganic Soil is composed of clay, silex, or sand, 

 with magnesia, saline and metallic compounds, as 

 gypsum, salts of soda, and potassa, and the oxides of 

 iron and manganese. Organic Soils are formed of 

 decayed animal and vegetable matter, with chemical 

 compounds of humus, carbon, and ammonia. 



II. SECTION.— Mineralogy. 



Mineralogy treats of those substances, whether 

 simple or compound, which exist naturally in the 

 crust of the earth, forming collectively the rocks and 

 strata which have been already spoken of under the 

 head of descriptive Geology ; and it accordingly de- 

 scribes the form, structure, composition, properties, 

 and uses of inorganic bodies. The term itself is 

 objectionable, being derived from a Latin and a 

 Greek root, a more correct word being " Metallo- 

 logy/' Its scope is, at present, tolerably extensive, 

 as it is found convenient to include under it all in- 

 organic natural substances, whether gaseous, liquid, 

 or solid. 



In pursuing satisfactorily this branch of en- 



