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Sect, VIII.] 



MINERALOGY 



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locality may be quitted. 



Among the minerals occurring in beds, we should more 



substances of 



that 



particularly notice coal and other 

 class, which have of late become so important for the 

 extension of steam navigation. Our pbipping daily 

 bring home specimens of coal or lignite from localities 



And 



occur 



where they were not previously known 



it may be here needful to state, as r »w well known 



geologists, that good coal is not confined to rocks of a 



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particular geological date, but that, the needful physical 

 conditions having obtained, it has been produced from 

 vegetable matter accumulated at different geological times. 

 When we have a cliff before us, there is little difficulty 

 in seeing that a coal-bed occurs amon^ others of sand 

 stone, shale, or other substances. 



N 



unfreq 

 iceous 



coal-beds are based upon clays, or argilla 

 which have a clayey character from exposure, and then it 

 sometimes happens, from the slipping and falling of the 

 general mass, that the real thickness and importance of 

 a coal-bed may not appear on a cliff. Thus it was at 

 Labuan, where now a valuable coal-bed about nine feet 

 thick is worked : when first seen on the coast it did not 

 appear more than eighteen inches thick. 



Of whatever geological age an accumulation of mud, 

 silts, sands, and gravels, now more or less consolidated as 

 shales, sandstones, and conglomerates, and contraning m- 

 terstratified coal, may happen to have been, it rarely 

 occurs that the bed upon which the coal itself reposes has 

 not some peculiar character, easily observed. In many 



nasfis we feel assured that this has arisen fi'om. these beds 



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