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CHAP. XXXIII. 



Limestone. Primary . 



THERE is one familiar character by which this rock is 

 distinguished from all others, but there is none by 

 which those of the primary and secondary classes can 

 be discriminated, when removed from their affinities 

 in nature. It has indeed been said that distinctions 

 might be found in their texture or composition, and in 

 the presence or absence of organized bodies. But, 

 out of a mass of facts by which this assertion is dis- 

 proved, the following will suffice. 



Primary limestone, lying under gneiss, in Sutherland, 

 contains bituminous beds; and the older limestones as- 

 sociated with argillaceous schist, thence called transition 

 rocks, contain organic fossils. Secondary limestones 

 are so often deficient in these remains, that it is unne- 

 cessary to name examples. Primary limestone is not 

 necessarily crystalline, since it contains earthy and com- 

 pact beds, in innumerable places. Secondary crystal- 

 line limestone, on the other hand, occurs in the Isle of 

 Mann, among earthy ones containing organic remains, 

 and also in Sky, where it is frequently of a snow white, 

 and undistinguishable from statuary marble. This im- 

 portant observation in geological philosophy, originally 

 made by myself, has since been confirmed in various 

 parts of Europe. But, in reality, the fact is sufficiently 

 common in other situations ; as crystalline limestone 

 also occurs not unfrequently near the contact of trap. 

 There is therefore no permanent or necessary mineral 

 distinction ; though, in particular instances, there are 

 often very strong ones : while these remarks will serve 

 to warn the student against pronouncing on the pri- 



