PRIMARY LIMESTONE. 369 



The varieties with curved lamellse are gene- 

 rally splendent in the fracture, arid contain mag- 

 nesia. Some of the finely granular, or large 

 granular varieties, also occasionally contain this 

 earth in very large proportion ; and the former 

 are, in some cases, known by the name of dolo- 

 mite. Magnesia occurs also at times in the 

 compact kinds ; but these varieties are scarcely 

 distinguishable without analysis. 



Under the head of Secondary Limestones, the 

 magnesian limestone occupies a distinct place, 

 on account of its important geological character 

 and connexions. In the case of dolomite this 

 seemed unnecessary. 



The colours of primary limestone are various; 

 and, from different modes of intermixture, there 

 results an infinite diversity of marbles, of which 

 a great many are distinguished by technical 

 terms which it would be fruitless to enumerate ; 

 as they are rarely descriptive, and will afford the 

 collector of specimens no assistance in arranging 

 his cabinet. The white varieties of a fine grain, 

 are well known as statuary marble : the coloured, 

 derive their tints from inflammable matter, or 



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