PHYSICAL PjROPERTIES OF SOIL. 249 



58 per cent, carbon are equal to . . . 827 lbs. 

 Leaving to be derived from air, . . . 956 " ; 



1783 " 



This is taking geine in its most insoluble state. The great 

 increase of solubility when combined with alkali would ren- 

 der the annual amount of water transpired equal to dissolv- 

 ing, as geine, all the carbon which has been added to the 

 plant. 



The advantage of a light porous open soil is now evident ; 

 it lets in air, it lets off steam. This steam, charged with 

 carbonic acid, acts on silicates, eliminates alkalies, waters and 

 feeds plants. Salts, geine, and barren pine plains, are the 

 elements of a western prairie. Nature never bestowed upon 

 man soil of greater capability of being made lastingly fer- 

 tile, than the sandy light soil of New England. 



296. It is evident that the terms of heavy and light, given 

 by the farmer to soil, do not refer to their absolute weight 

 (293). These distinctions depend on firmness or consistency 

 of soil. This produces a very marked difference in the fer- 

 tility and tillage of land. The terms light and heavy, mean 

 lighter or heavier to work. It is well known that clay lands 

 are heavy to work, sandy soil the lightest and easiest, next 

 to this is a soil containing a small portion of geine. All 

 light soil becomes heavy when wet, but it is a well-ascer- 

 tained fact, that heavy soil always becomes lighter by frost. 

 Hence the reason of breaking up with a plough before winter. 

 Moist earth then becomes frozen, and its particles being 

 driven asunder by frost, it becomes lighter, in truth it has 

 been found that the consistency of clay is diminished nearly 

 one-half by frost, and loamy clay, one-half to two-thirds. It 

 is essential to this change from heavy to light land, that the 

 11* 



