108 ORGANIC REMAINS. 



point out a general turbulence in the waters at the period of their de- 

 position. I must not go further into the cause of this exception, than 

 to state, that if, as is believed, nearly all these vegetables grew on land, 

 and were thence transported to the sea, they would naturally be broken 

 to pieces by that operation. 



The chemical changes which fossil plants have undergone are 

 various, and seem partly to depend on peculiarities in their original 

 structure, and partly on the nature of the strata which enclose them. 

 Thus the fibrous wood of dicotyledonous plants found in the limestone 

 of Malton, appears as a brown carbonaceous mass, much traversed by 

 calcareous spar : that which lies in the calcareous gritstone beneath, is 

 sometimes impregnated with siliceous matter ; but in the aluminous 

 shale of Whitby, such wood is partly converted to jet, and partly filled 

 with pyrites, or calcareous spar. The ferns and other monocotyle- 

 donous plants which lie in the sandstones and shales of our coal districts, 

 are very differently preserved. Whatever be the kind of plant which 

 is found in shale or fine-grained gritstone, all that remains of its sub- 

 stance is coal, often of the purest and most inflammable quality. In this 

 case we may suppose the decomposition of the vegetable matter to have 

 been slow and gradual ; and being operated under a close covering of 

 shale or gritstone, the resulting chemical substances were prevented 

 from escaping, and made to combine into a new inorganic compound, 

 coal. The same plants lying in coarse sandstone retain very little of 

 their original substance, perhaps on account of the porosity of the rock, 

 which might both favour the decomposition of the plant, and hasten the 

 escape of the resulting gases, and soluble matter. 



After investigating the changes which have happened to fossil plants, 

 no reasonable doubt can be entertained as to the vegetable origin of all 

 our beds of coal. Perhaps the different qualities of coal may be in a 

 great degree owing to the nature of their constituent plants. 



The hard parts of invertebral animals, which are preserved in the 

 earth, are closely allied to each other in chemical composition. In all 



