236 GEOLOGY AND CHEMISTRY OF SOILS. 



of lime, with sand and fossil shells, which are derived mostly 

 from the gault or wealden rocks. These resemble the clayey 

 soils of the tertiary formation. 



2. Oolitic soil is remarkable for the quantity of calcare- 

 ous earths which it contains. It is derived from argillaceous 

 limestones, clays and marls, and in consequence of the great 

 quantity of fossil remains, is a very fertile soil. 



3. Salifcrous or sanchtone soil is derived from sandstone 

 rocks. It is composed of argillaceous, siliceous or calcareous 

 matters, often highly charged with red oxide of iron, which 

 gives to the soil a red appearance. It is, however, of every 

 shade of color, and variety of texture and composition, vary- 

 ing from light sandy loams to stiff marly clays. The sand- 

 stone soil of New England is either colored red as in the 

 valley of the Connecticut river, or gray. It is warm, dry and 

 capable of being made very fertile. The rocks from which 

 this soil is derived often contain gypsum and common salt, as 

 at Salina, New York, and on this account favor the growth of 

 those plants which require a large quantity of soda. Ow- 

 ing to its texture, it is particularly favorable to Indian corn, 

 and the tap-roots, beets, carrots and turnips. The magnesian 

 variety is much more retentive of water, and constitutes a 

 very fertile soil. 



4. Carboniferous soil is derived from three kinds of rock. 

 1. Thq shales of the coal beds, consisting mostly of argilla- 

 ceous earth with vegetable remains and sandstones. 2. Car- 

 boniferous limestone, also called mountain limestone, which 

 is so filled with the remains of small animals, Enchrinites, as 

 to receive the name of enchrinal limestone. 3. The old red 

 sandstone, which does not differ essentially from the red sand- 

 stone of the preceeding class. The soil will of course vary 

 with the kind of rock. 



5. Silurian or grat/iaackc soil oug\n:ites from an extensive 

 class of rocks, under the name of graywacke, graywacke 

 slate and shale. It is composed of sand, clay and calcare- 



