CLASSIFICATION OF SOILS. 57 



nearly all originally formed from this rock. Many of 

 these are very poor; but there are some sandstones 

 which make most excellent soils, as rich as any that 

 are cultivated. In particular cases they contain so 

 much lime as to be nearly marls, and then form very 

 fertile soils. Very many sandstones crumble away 

 quite readily, some showing the action of the atmo 

 sphere almost immediately upon exposure. For this 

 reason the soils are ordinarily of good depth. 



2. Limestone is also common, and there are few 

 places where a teacher can not find some to exhibit to 

 his scholars. It is found of all colors from white to 

 black, and makes a great variety of soils. As a ge 

 neral rule these soils are good, and capable of bearing 

 very excellent crops. There is much variation among 

 the limestones as to ease of decomposition. Many of 

 them form a deep soil very soon, but there are some of 

 the blue mountain limestones which decompose with 

 exceeding slowness. On these the soil is thin, but 

 usually of rather good quality, especially for pastures. 



3. Clay is the principal ingredient in roofing slate, 

 in school slates, and in what are called shales. Be 

 side this, as is well known, it exists in large beds, 

 from which are made pipes, bricks, tiles, etc. etc. 

 Whenever it occurs largely in soils, they are stiff, 

 tenacious, and nearly impervious to moisture. In 

 consequence water remains on the surface, and makes 

 them wet, difficult to plough, and hard to cultivate in 

 any way. They are, however, usually of good quality, 

 and by proper skill may be made most valuable. 



Some writers have classified soils, according as they 

 contained more or less of one of these. First would 

 be a sand, then a sandy loam, then a clay loam, a stiff 

 clay, and finally a brick or pipe clay, the last being 

 too stiff for cultivation. Soils in which lime existed 

 largely, would be called calcareous. Where there 

 was more than 20 to 25 per cent, it would be a marl. 



