No. 7. DEPARTMENT OF AGRICULTURE. 247 



determination of tlie amounts of nutritive elements extracted by 

 the two media will modify this. 



Before this assemblage it would be presumption on my part to 

 attempt to discuss the elements that make for continued fertility. 

 I am sure, however, that we stand on common ground when I as- 

 sert that rock dirt is not soil, any more than peat, and to be arable, 

 a soil must in addition to from five to ten per cent, of organic matter, 

 possess such a porosity and texture as will allow of the circulation 

 and retention of at least the same volume of water. 



The plant food, which is necessary for a generous growth of vege- 

 tation throughout periods of excessive rain and of protracted drought, 

 is made soluble and available by the action of the atmosphere on 

 the soil and by humus collected from decaying vegetable matter. 

 It consists of the alkalies and phosphoric acid which are found in 

 limestone, sandstone and shales from which the soils are derived. 

 The richest supply is in the limestone, whose origin is in the deep 

 sea, which contains the decomposed organic matter and the orig- 

 inal calcareous material secreted by shell and coral remains built 

 beneath the sea. Wherever its decomposition furnishes a soil in 

 place, there the fertility reaches a high limit. All over the world — 

 the Great Valley, the Little Valley, Morrison's Cove, Genesee Valley 

 — limestone soils are of the highest degree of productiveness, not 

 only Vt^hen cultivated, but even when undisturbed by artificial agents, 

 as is witnessed by the "Oak Openings" and other luxuriant native 

 forest growth subsisting thereon. Limestone is easily acted on by 

 the atmospherical agents and by the solvent power of the waters, 

 which readily dissolves material and renders it capable of assimila- 

 tion by the myriads of rootlets which easily penetrate its soil; but 

 in that process nine-tenths of the rock is dissolved and carried 

 away to the sea. The residual soil of a limestone is composed of 

 clay and sand, only one-tenth the volume of the original rock. 



Sandstones are more porous than limestone and are less soluble; 

 they lose, therefore, less of their constituent grains and are more 

 readily attacked by the mechanical agencies we have mentioned, 

 than are limestones. Their soils are loose, very porous, and unless 

 replenished by natural drift from the limestones or the shales, 

 would be unprofitable to agriculture, because the soluble ingre- 

 dients, the nutritive elements, are lost by the descent of the ground 

 waters. Sandstone soils, too, are more likely to be deficient in the 

 alkalies than are the limestones and we therefore find native, only 

 a forest growth of stunted timber of inferior kinds. 



Shales furnish a heavy clayey waste, because they are made of 

 comparatively insoluble clay with a cement of lime or sand, and, 

 though rich in the alkalies, are poor in phosphoric acid. They yield 

 readily to the attack of the atmosphere, furnishing a residual clay 



