210 AMBKICAN POMOLOGY. 



tion and climate, may not be so readily overcome ; they 

 have already been alluded to ; and even in them we may 

 hope for improvement vrith the advance of science. 



Different soils may be designated as porous and compact. 

 Leaving out of view for the present, their chemical com- 

 position, let us look to their mechanical structure. Porous 

 BoOs are composed of materials that always allow of the 

 escape of superabundant moisture ; they are generally un- 

 derlaid by beds of diluvial gravels, or by rocks of a po- 

 rous character. Such lands are peculiarly adapted to or- 

 chard planting. The compact soil, on the contrary, is 

 made up of the finest materials, among which alumina 

 largely predominates. Such are called clayey soils or 

 clays, and are among the most valuable upon the surface 

 of the earth, jaot because alumina is a component of vege- 

 tation, but because the elements associated with it, are all 

 of them in a state of extreme comminution. 



Clays are compact soils, not only by reason of the fine- 

 ness of their particles, but because the predominating 

 alumina swells and becomes j>asty when it is wet, and 

 thus prevents the passage of water through them. On 

 this account, soils that are too compact, especially if they 

 be underlaid by stiff clay subsoils, are not so well adapted 

 to orcharding as those that are more porous. This is es- 

 pecially true of level lands, upon which water accumulates, 

 to the great injury of the fruit-trees planted upon them ; 

 but even in hilly situations, with good natural surface 

 drainage, the excess of clay is indicated by a " spouty " con- 

 dition of the surface. So many varieties succeed in clayey 

 lands, however, and some are so superior in their products 

 when planted upon clays, that we need not be discouraged 



