238 GEOLOGY AND CHEMISTRY OF SOILS. 



Soils from tlie primary rocks are most abundant in New 

 England. They are derived mostly from the decomposition 

 or decay of granite, gneiss, mica slate, argillaceous, talcose, 

 and hornblende slates. These rocks contain the ingredients 

 of nearly all soils ; silica, alumina, lime, magnesia, oxide of 

 iron and of manganese, to which may be added the alkalies, 

 potassa and soda. They are generally distinguished by the 

 minerals which they contain, and which exist either in large 

 or fine particles. The principal minerals are mica, feldspar 

 and quartz. The mica is seen in thin shining scales ; the 

 quartz in angular or rounded pebbles, and the feldspar in 

 white and earthy particles, more or less covered with oxide 

 of iron, or vegetable mould. These ingredients may be de- 

 tected by mixing the soil in water, agitating it a while, and 

 pouring off the finer portions. 



1. Argillaceous slate soil is derived from a rock well 

 known from its structure, and from its use for the purpose of 

 roofing buildings. It exists in very great perfection in Ber- 

 nardstown, Mass. and Guildford, Vt. The color of this soil 

 resembles the slate, which is dark brown, almost black. It 

 is a poor soil in many places, especially where the rock ap- 

 proaches near the surface, but when the disintegration has 

 proceeded to a greater depth, it is capable of being made a 

 very good soil. It is composed almost entirely of argillace- 

 ous earth, mixed with a small quantity of silex. 



2. Limestone soil. The primitive limestones which are 

 interstratified with the slates, give rise to a variety of soil, 

 which does not differ materially from the talcose and mica 

 slate soil, as it appears from analysis, that some of them do 

 not contain carbonate of lime in any considerable quantities. 

 This may be due to the action of crops, or to the fact that 

 the detritus of other rocks have been brought over them, and 

 constitute their principal mass. 



Some varieties of this soil contain carbonate of lime, others 



