284 SOILS - 



tive of calcareous lands ; and these, as will be more fully shown 

 below, are almost always highly productive. 



From both points of view, then, the favorable judgment 

 passed upon black soils by practical men is justified. 



But it is not necessarily true that soils showing no obvious 

 black tint are poor in humus; for in strongly ferruginous or 

 " red " soils its tint is frequently wholly obscured, though 

 when still visible it gives rise to the laudatory name of " ma- 

 hogany land," which every farmer considers a prize. 



Of course then it would be wholly incorrect to judge of the 

 agricultural value of land from its humus-content alone; for 

 its color may be entirely imperceptible and yet its amount and 

 nitrogen content be fully adequate to the requirements of 

 thrifty vegetation. Gray and even whitish soils very fre- 

 quently fall within this category in the arid region. 



The black tint is also favorable to the absorption of the 

 sun's heat, and is therefore conducive to earlier maturity than 

 is to be looked for in light-tinted lands similarly located. 



Wollny (Forsch. Agr. Phys. Vol. 12, 1889, p. 385), dis- 

 cusses the influence of color on soils in relation to moisture and 

 content of carbonic acid. The results show in general simply 

 the effects due to increase of temperature when the soils are 

 either darker-colored throughout, or made so superficially. 



" Red " Soils. Next to a black soil, a " red " one will usu- 

 ally command the instinctive approval of farmers. The cause 

 of this preference is not as obvious as in the case of the black 

 tints; but the general consensus of opinion requires an ex- 

 amination of its claims. It is of course easy enough to adduce 

 examples of very poor " red " soils, derived from ferruginous 

 sandstones that supply little else than quartz and ferric hy- 

 drate ; the Cotton States supply cogent examples in point, as 

 do also the lower Foothills of the Sierra Nevada of Cali- 

 fornia. It is not, therefore, the iron rust or ferric hydrate that 

 renders the land productive; but its presence is a sign of some 

 favorable conditions. First among these is, that ferric hydrate 

 cannot continue to exist in badly drained soils; a " red " soil 

 is therefore a well-drained one, and this is probably one of the 

 chief causes of the popular preference. The " white land " 

 sometimes seem in tracts otherwise colored with iron, is dis- 

 tinctly inferior in production to the red lands ; and examination 



