208 GEOLOGY AND CHEMISTRY OF SOILS. 



ever, not in its pure or caustic state, but combined with acids, 

 forming with carbonic acid the carbonate of lime (marble), 

 which is the most abundant. In this form, it constitutes about 

 ^ part of the crust of the globe. The sulphate (common plaster) 

 is next in abundance, and the phosphate is diffused through all 

 soils, and is the source from which animafls obtain their bones. 

 The pure or quick lime is generally obtained by heating the 

 carbonate in kilns, until all the carbonic acid is driven off. It 

 will then unite with water, and form a white bulky hydrate, 

 called slacked lime, used for mortar. 



The quantity of lime, found in the soils of this country, is 

 generally very small. From an analysis of the soils of Mas- 

 sachusetts, as contained in the report of Prof Hitchcock, 

 lime, in the form of carbonate, sulphate and phosphate, does 

 not upon an average exceed 3 per cent. The sulphate is 

 the most abundant, varying from 0.1 to 3.9 per cent. 



The carbonate of lime, with the exception of one soil, in 

 Truro, which contains 21.3 per cent, varies from mere traces 

 of it, to 6 per cent, ; but generally there is much less than 

 2 per cent., and not one soil in twenty, contains a single par- 

 ticle of lime in the state of carbonate. The amount of phos- 

 phate is not accurately determined, but the proportion in 

 most soils is less than 1 per cent. The soils of Rhode Isl- 

 and, according to the analysis of Dr. C. T. Jackson, do 

 not, upon an average, contain 1 per cent, of all the salts of 

 lime, and scarcely 1 per cent, is found in the soils of New 

 Hampshire. 



Soils from the Western, Middle, and Southern States, al- 

 though from lime-stone regions, rarely contain a larger pro- 

 portion of lime, in any form than is found in New England. 

 It appears from an analysis of five specimens of soil from Il- 

 linois and Ohio, that all the salts of lime amounted, upon an 

 average, only to 4.9 per cent. 



In other countries, soils are frequently described, contain- 

 ing from 6 to 30 per cent, of the carbonate alone. In this 



