THE COLORS OF SOILS. 



285 



will generally show that from some cause, such white lands 

 have been subjected to the watery maceration which proves so 

 injurious (see chap. 3, p. 46, chap. 12, p. 231). 



That finely-diffused ferric hydrate has a very high power of 

 absorbing moisture as well as other gases of the atmosphere, 

 has been shown in the preceding chapter; it stands in this re- 

 spect next to humus itself, and hence highly ferruginous soils 

 need not contain as much humus as " white " soils from this 

 point of view. Like humus, also, it renders heavy clay soils 

 more easily tillable. 



Origin of Red Tints. Where crystalline rocks prevail, the 

 red tint usually indicates the derivation from the weathering of 

 hornblende; implying also, outside of the tropics, the presence 

 of sufficient lime in the land. Such lands are naturally pre- 

 ferred to those of lighter tints derived from purely feldspathic 

 rocks (see chap. 3, p. 32), although they may be poorer in 

 potash than the latter. 



But the red tint has also its intrinsic advantages in the more 

 ready absorption of the sun's heat by the colored than by a 

 white surface. This is probably the chief cause of the higher 

 quality of wines grown on red hillsides in the middle and 

 northern vine districts of Europe, where everything that aids 

 earlier maturity is of the greatest importance. The function 

 of ferric oxid as a carrier of oxygen (chap. 4 p. 45) prob- 

 ably also aids nitrification. 



" Yellow ' lands owe their tint, of course, to smaller 

 amounts of ferric hydrate, but share more or less in the ad- 

 vantages of the " red." 



White soils, or more properly those having very light gray 

 tints, are not usually looked upon with favor, especially in the 

 humid region. The causes of the unfavorable judgment cur- 

 rent among farmers in respect to white soils has already been 

 partially explained in the discussion of the black and red tints. 

 The light color means the scarcity or absence of both humus 

 and ferric hydrate, and usually implies that the soil has been 

 subject to reductive maceration through the influence of stag- 

 nant water ; reducing the ferric hydrate to ferrous salts, oxidiz- 

 ing away the humus, and accumulating in the form of inert 

 concretions most or all of the lime, iron and phosphoric acid of 

 the soil mass (see chap. 3, p. 46, chap. 10, p. 184). The 



