52 EARTHS AND SOILS. 



in such a manner as to supply what is lost by evapora- 

 tion, and the consumption of plants. 



" When soils are situated immediately upon a bed of 

 impervious rock or stone, they are much sooner rendered 

 dry by evaporation, than when the subsoil is clay or 

 marl. A stony subsoil, w^hen in a position approaching 

 to the horizontal, is, in general, prejudicial, and, if the 

 surface soil be thin, usually occasions barrenness ; unless 

 the rock should be limestone, and then the soil, though 

 thin, is distinguished for its fertility. 



"2. A porous subsoil, if not carried to an extreme, 

 is uniformly of great advantage, not only by its admitting 

 the fibrous roots of vegetables to extend deeper, in search 

 of moisture and nutriment, but also from its carrying oft 

 all superfluous moisture, which is less perfectly done ar- 

 tificially, by the expensive operation of hollow-draining. 



" Below clay and all the variety of loams, an open 

 subsoil is particularly desirable. It is favorable to all the 

 operations of husbandry ; — it tends to correct the imper- 

 fections of too great a degree of absorbent power in the 

 soil above ; — it promotes the beneficial effects of ma- 

 nures ; — it contributes to the preservation and growth of 

 the seeds ; — and insures the future prosperity of the plants. 

 Hence it is, that a thinner soil with a favorable subsoil, 

 will produce better crops than a more fertile one, incum- 

 bent on wet clav, or cold or nonabsorbent rock. 



" Lands whose substratum consists of clean gravel or 

 other silicious earths, can bear but little sun, owing to 

 their not having a capacity of retaining moisture, and 

 their generally possessing but only a shallow surface of 

 vegetable mould." — Sinclair''s Code of Agriculture. 



The difficulties resulting from a retentive subsoil are 

 likely to be obviated, in a great measure, by improve- 

 ments of recent introduction ; — viz., furrow-draining, and 

 subsoil ploughing. The first drains off the surplus water 

 from the surface soil, and the latter deepens the soil, and 

 facIUtates the passing off of surplus water. 



