34 



AMERICAN VINES. 



carbonate of lime exists finely pulverized, mixed with 

 siliceous grains and coated with clay. In the former, not- 

 withstanding the high percentage of silica, the roots are 

 in immediate contact with carbonate of lime ; in the second, 

 on the contrary, the contact only exists at a few points, 

 and the clay in some cases coating the small grains of 

 limestone isolates them from the roots and renders them 

 less attackable by water charged with carbonic acid, and 

 so diminished its detrimental effect. The ameliorating 

 effect of clay was pointed out by several observers, notably 

 Cazeaux-Cazalet and Chauzit. We must also take into 

 account the state of division of the carbonate of lime in 

 the soil; in very small grains it offers a greater surface 

 than when in large grains. In porous and soft grains 

 (chalk) it is more noxious than when the grains are 

 compact or crystallized. 



It results from this, that the different states under which 

 carbonate of lime is found in soils have different properties. 

 Certain limestones are very easily attacked by dilute acids, 

 while others are less so. This is shown in the following 

 table, taken from Houdaille and Semichon: 



RATE OF SPECIFIC ATTACK OF LIMESTONES 



