ON THE ORIGIN OF COAL. 165 



much the same, but as soon as they become red, 

 and are mixed with beds of limestone, the seams 

 become of little value, thus showing that the 

 condition of the waters had some connexion with 

 the production of the seams of Coal ; for we find, 

 that the strong currents of the lower Coal field 

 were not favourable to the formation of thick 

 and numerous seams of Coal, but that the 

 tranquil and quiet waters of the middle one 

 were ; while the w^aters of the upper field, although 

 equally quiet and tranquil, having been charged 

 with peroxide of iron, and carbonate of lime, 

 were not favourable to the formation of thick 

 and valuable seams. Rocks highly charged with 

 peroxide of iron, are generally sparingly stored 

 with animal remains, whilst those containing 

 carbonate of lime, are, for the most part, full of 

 them. We thus see, that the distribution of 

 plants and animals varied, according to the state 

 of the waters they lived in. The general absence 

 of fossil plants in limestones of all ages, has never 

 yet, to my mind, been satisfactorily accounted for. 



The occurrence of thick seams of Coal lying 

 amidst the most tranquil of aqueous deposits, and 

 the rareness of such seams in the coarse gritstones 

 of the lower field, seem to prove anything but 



