LIMESTONES 



127 



Meelianically included materials, as sand and clay, are com- 

 mon, giving rise to siliceous and argillaceous varieties. The so- 

 called hydraulic limestone 

 is one containing 10% 

 and upwards of these 

 impurities, and which 

 when burnt and ground, 

 forms a cement character- 

 ized by its property 

 of setting under water. 

 Many limestones, like the 

 dolomitic varieties in Cook 

 County, Illinois, contain 

 so large a proportion of 

 bituminous matter as to 

 give off a distinct odor of 

 petroleum when struck 

 with a hammer, or even to 

 become blackened on the 

 surface by its exudation 

 when exposed to the weather. Others contain phosphatic matter, 

 and pass by insensible gradations through what are known as 

 phosphatic limestones to true phosphates (phosphorites, etc.). 



EiG. 12. — Microstrueture of fossiliferous 

 limestone. 



Chemical CoMPosiTioisr of Limestones and Dolomites 



CJONSTITUmSTS 



Carbonate of lime (CaCOg) . . 

 Carbonate of magnesia (MgCOg) 

 Oxides of iron (FeO and FegOs) 

 Oxide of aluminum (AlgOg) . 

 SiUca (Si02)2 and insol. silicates 

 Potash (KgO) ... 



Soda (IsTagO) 



Water (HgO) 



Sulphate of lime (CaSOg) . 

 Organic matter 



Totals ....... 



Q 



■♦5 rt 



id 5 



f~^ TO 





53 g 



98.00 



0.57 



98.57 fc 



u 



03 S 





54.62 fa 

 45.04 



|o.23 



^ ta ei ta 



41.88% 

 24.55 



} 



4.03 



29.93 

 0.22 

 1.12 



99.89 fo 



101.73^ 



6 



oja OS 

 — '3 >• 



g -Si 



IS cj 3 



W 



72.95% 

 3.84 



4.50 

 14.79 



1.75 

 1.46 



100.63% 



o 



o o 2 



96.60 % 

 0.13 

 0.98 

 • . . • 

 0.50 

 0.31 

 0.40 

 0.96 



99.88 % 



