CHAPTER XCI. 



CALCAREOUS MANURES. 



l^TINERAL Sources. Marble, chalk, dolomite and kankar 

 (or glutting] are the commonest minerals containing 

 lime. Limestone rocks are rarely pure calcium carbonate 

 (CaCO 3 ). They usually have some Magnesium Carbonate 

 (MgCOs), and also clay, silica, iron and organic substances, 

 combined with them. When a limestone contains more 

 than 23 per cent, of MgCO 3 it is called dolomite. When it 

 contains fossil remains of animals, it has a certain proportion 

 of CasPgOs combined with it. It occasionally occurs in a 

 pure crystalline state, as calcite or calcspar. As stalactite 

 and stalagmite it is found deposited in springs. Marble and 

 chalk are also nearly pure CaCOs. Limestones contain fossils 

 more often than dolomites, and they are more easily scratched, 

 and they effervesce more readily with hydrochloric acid. 

 Limestones are found in all geological formations, as crystalline 

 limestones and marbles in old formations, as chalk in the middle 

 age of the geological era, and as kankar or limestone nodules 

 in alluvial regions. Limestone rocks are often associated with 

 ^gypsum, the former undergoing a local conversion in contact 

 with decomposing iron pyrites (FeSs). Where gypsum occurs, 

 rock-salt may also occur. 



919. Marble, dolomite and kankar^ occur in almost 

 all the districts of the Madras Presidency; in Khasia 

 and Jaintia hills, in Assam ; in the Sambalpur, Raipur, 

 Jabbalpur, Nagpur and Wardha districts of the Central 

 Provinces j in Kathiwar in the Bombay Presidency; and in 

 Baroda, Hyderabad, Mysore, and Burma. Kathiwar marble 

 is used even in Calcutta for building purposes. The best 



