212 PRIMARY LIMESTONE. 



associations ; appearing to be peculiarly attached to 

 no rock, whereas there is a predominant, though not 

 a constant, affinity and order, among many others of 

 the primary strata. 



It is almost unnecessary to say, that it presents 

 many varieties of texture, from the large crystalline to 

 the most minute saccharine grain, and from a smooth 

 and flat conchoidal fracture, to one of an earthy and 

 dull aspect. It often differs from the secondary, in 

 containing various imbedded minerals ; though not so 

 often as to form a sure ground of distinction. These 

 will be found enumerated in the Classification of Rocks: 

 while their existence proves, demonstrablv, that the 

 strata in question have been fused ; giving occasion ? 

 as in micaceous schist, to the crystallization of similar 

 igneous minerals. Its well-known chemical properties 

 render a definition superfluous: but the student must 

 recollect, that the indurated kinds do not readily ef- 

 fervesce unless previously powdered. 



If it is superfluous to mention its ceconomical uses, 

 yet, as it often contains alternating laminae of other 

 rocks, so as not to burn readily into lime, it is often 

 neglected, even when fit for all the purposes of ma- 

 sonry or agriculture. Being a limited rock, it is 

 not very productive of metallic veins ; but it is 

 said that lead, manganese, silver, zinc, and gold, 

 have been found in it. How widely it is used as marble, 

 I need not say; while its ornamental varieties are 

 amply recorded. 



