100 W A L L } S M A N if A t, 



are aqueous, or from water, This is the Onty 

 division necessary to the farmer. It is the division 

 taught and demanded by agricultural geology < 



The first class (or those from fire), includes all 

 highly crystalline rocks, such as granite, gneiss^ 

 sienite, greenstone ; it includes, also, basalt and lava. 

 The products of volcanos, both ancient and modern, 

 should be placed ih the same class, 



The second (or that from water), includes sand, 

 gravel, rounded and rolled stones of all sizes, pudding 

 stones, conglomerates, sand- stones, and slates, When 

 these various substances are examined^ a large part 

 of the sand is found to be composed essentially of 

 the ingredients of the igneous rocks, This is true, 

 also, of sand- stone, slate, and boulders. 



FORMATION OF DEPOSITS. . 



There are large deposits, or formations, in various 

 districts, composed almost entirely of some of the 

 chemical constituents of the igneous rocks^ united 

 with an ingredient of air, These constituents are 

 lime and magnesia ; the portion derived from air is 

 carbonic acid, forming, by their unioiij carbonates of 

 lime and magnesia. Marble, limestone^ and chalk,? 

 belong to this formation, The lime, originally a 

 part of the igneous rocks, has been separated, and 

 combined with air by animals and plants, by a vital 

 process called secretion. The modern production of 

 the carbonate of lime, is still going on under the 

 forms of shells and corals. But limestone is truly 

 a salt, rather than a rock, and should be classed with 

 the salts. 



The transportation, or distribution of the soil, by 



