160 PLAIN AND PLKA8ANT TALK 



GEOLOGICAL DEFINITIONS. 



Mant terras, in general use among scientific men, and 

 usually employed in agricultural works, are obscure to 

 young readers. For their sakes we will explain some of 

 them ; and shall not be angry if old men profit by the 

 explanation. 



Soil. — The surface-earth, of whatever ingredients it may 

 be composed. It may be a clay-soil, a sand-soil, a calcareous 

 soil, as the surface is composed of clay, or sand, or clay 

 strongly mixed with lime, etc. 



Subsoil. — The earth lying below the ordinary depth to 

 which the plow or spade penetrate. Sometimes it has 

 hardened by the running of the plow over it for a series 

 of years ; then it is called pan^ as hard-pan, clay-pan, etc. 

 It is sometimes of the same nature as the top-soil, as in clay- 

 lands ; in others it is a different earth ; as when a coarse 

 gravel underlies vegetable mold, or Avhen clay lies 

 beneath sandy soil. 



Subsoil Plowing. — In ordinary plowing, the share runs 

 from five to seven inches deep. A plow has been con- 

 structed (called subsoil ploAv), to follow in the furrow, and 

 break up from six to eight inches deeper — so that the 

 Avhole plowing penetrates from ten to sixteen inches. 



Subsoil Plow. — A plow having a narrow " double share^ 

 or a small share on each side of the coulter, and no mold- 

 board." It is designed to break up and soften the subsoil, 

 but not to bring it up to the top. 



Mold. — A soil in which decayed vegetable matter 

 largely predominates over earths. Thus, leaf-mold is soil 

 principally composed of rotten leaves; dung-mold, of 

 dung reduced to a fine powdery matter; heath-mold, a 

 black vegetable soil found in heath-lands; peat-mold, 

 forest-mold, garden-mold, etc. 



Loam. — Clay, or any of the primitive earths, reduced to 

 a mellow, friable state by intermixture of sand^ or vegeta- 



