SECONDARY LIMESTONE. 447 



Effervesces readily and burns to lime which is 

 easily slacked. 



A. Crystalline ; more or less perfect. 



a. Granular. 



b. Granular splintery. 



A white variety occurs in Sky, not to be 

 distinguished from primary limestone (marble 

 for sculpture). They are however more fre- 

 quently grey. In some cases, and not un fre- 

 quently near trap, crystalline particles, or por- 

 tions, more or less extensive and conspicuous, 

 are found imbedded in, or intermixed with, lime- 

 stone of an earthy texture. 



B. Compact, with a smooth fracture more or less 

 glossy. 



a. Flat, splintery. 



b. Splintery and small conchoidal. 



C. Thin laminar, scarcely schistose. 



D. Fibrous, or prismatic. 



a. Fibrous, more or less minute : the 



fibres simple, parallel, and coalescing; 

 sometimes, slightly undulated. The 

 lustre is occasionally silky, and the 

 colour white ; forming satin spar. 



b. Fibrous, the fibres ramifying; coa- 



lescing, and with a pseudo-organic 

 structure. 



