518 PAL-EONTOLOGIOAL REPORT OF GEOLOGICAL SURVEY. 



scarcely grows out of the reach of marine water. There is in those re- 

 mains of fossil plants very few of the species now living along the 

 Mississippi and the Ohio rivers. A new deposit of leaves, now, would 

 show a great difference between the vegetation of this last with the for- 

 mer one. Such difference in the recent formations may be observed 

 in many places. From this it seems rational to admit, that two beds 

 of coal, separated by various and sometimes thick strata of another 

 nature, ought to present certain differences, in the remains preserved^ 

 their shale — some peculiar character which may enable a palaeontolo- 

 gist to identify each of them, or to know their geological level at eve- 

 ry place where it is possible to see them open for a careful examina- 

 tion. 



Though the exposition of those principles is new, the best living 

 geologists — Lyell, Brongnart, Burat, &c. &c. — have acknowledged 

 their truth. For they have admitted that the palaeontology of the 

 shales would in time direct the identification of each bed of coal. M. 

 de Humboldt, himself, says in his Cosmos : " That where several series 

 of coal strata lie over one another, the genera and species of plants 

 are net generally mixed, but arranged in a peculiar order for each bed." 



The roof shales are subjected to some variation like the other for- 

 mation, but they are rarely liable to modifications that, can prevent 

 their identification. Their thickness varies according to the depth of 

 the water in which they are found. This depth of water, as we have 

 before stated, would be nearly the same through the whole extent of 

 a coal basin, if there had not happened some local depressions, caused 

 either by volcanic commotions or by peculiar sinkings of the floating 

 mass of vegetation. Those local depressions have caused the separa- 

 tion of a bed of coal into two or more branches^ and sometimes its en- 

 tire disappearance amoDg high banks of black shales. Such cases are 

 not very rare. Then the shales, though thick, being of the same age, 

 and their inhabitants not having been subjected to any destructive 

 change, they preserve identity in their fossil remains. 



A short depression, or perhaps an accidental inundation of short du- 

 ration, makes upon marshes the beginning of a formation of shales, 

 which, if it is soon stopped by a new vegetation, produces in the bed 

 of coal a separation or a clay parting. As these partings are formed 

 upon the surface of a vegetable stratum, they ought to be generally 



