CHEMICAL CLASSIFICATION OF SOILS. 247 



Tests. Take a small quantity of the soil ; heat it to 300° 

 F. and then place it in a glass and cover it with pure water ; 

 drop on a few drops of hydrochloric acid ; if bubbles of gas 

 come up through the water it contains carbonate of lime. 

 The pebbles will also show of what the soil is principally com- 

 posed. The chalky variety is white, and reflects the heat 

 more than the darker varieties. 



Degree of fertility. Calcareous soils when combined with 

 clay, with other earths and vegetable matters, are among the 

 most fertile soils. If combined with siliceous sand and grav- 

 el, they are light, loose and often unfertile ; but when com- 

 bined with aluminous earth, they are the richest soils in all 

 wheat-growing countries. 



Mode of improvement. As pure calcareous sand or gravel 

 is too friable and loose for the support of vegetation, it may 

 be improved by adding clay-loam, or even pure clay ; and 

 sometimes sand and peat-muck, are highly valuable. Lime 

 tends to exhaust the humus of the soil; large quantities of 

 yard-dung or vegetable matter should therefore be supplied 

 to keep up the fertility. 



Crops. Tillage crops are best adapted to calcareous soils, 

 such as peas, turnips, barley, clover, wheat and Indian corn. 

 They give a peculiar sweetness to the grass which grows 

 upon them, or rather favor the sweet grasses, and hence are 

 excellent soils for pasture lands. 



4. The magnesian soils which result from serpentine rocks, 

 and magnesian limestones are very fertile soils, but not of 

 sufficient extent to be farther noticed in this place. 



5. Peaty soils are composed of large quantities of vegeta- 

 ble matter mixed with earthy ingredients, lime, silica, alu- 

 mina and oxide of iron. They abound in the eastern part of 

 Massachusetts, and in most temperate regions of the earth. 



Origin. These soils originate from growing vegetables, 

 such as mosses in swamps where there is so much water that 

 the roots, leaves and branches of trees accumulate, and are 



