520 PALiEONTOLOGICAL REPORT OF GEOLOGICAL SURVEY. 



careful study. The animals of the limestone belong, evidently, to the 

 sea, and are brought in with it. In a change of level they are des- 

 troyed as individuals, not as species. Nevertheless, after a length of 

 time, a new invasion of the sea ought to bring with it, upon the coal- 

 fields, other species, since its neighboring sea and its inhabitants ought 

 to have been subjected to changes. 



Thick beds of limestone, interposed in many places between beds of 

 coal and shales, offer the most certain indications of the slowness of 

 the oscillations in the level of the coal-fields at the time of their for- 

 mation. Not only the great number of species — the myriads of ani- 

 mals of which the remains have been literally heaped together — but the 

 introduction of madrepores, and their constructions, marked in the 

 limestone strata, call for an inconceivable length of time. 



5th. THE SANDSTONE. 



In its general appearance, thickness, and composition, this formation 

 is the most unreliable of all. A substance, of which the elements 

 have been transported and intermixed by currents, can never be an 

 homogeneous one, especially when these currents are abnormal, the re- 

 sult of a cataclysm, and have exercised their action over a very extend- 

 ed surface, following numerous diversified phenomena. The move- 

 ments of the waters, which have brought and deposited the sand, are 

 made appreciable not only by the nature of the strata, but by traces 

 of remarkable erosions. ' In some places the immediate contact of the 

 sandstone with the coal cannot be explained but by an erosion of the 

 beds of shales and limestones which were extended upon it. Even the 

 coal has been sometimes swept away, then bruised, and deposited again 

 with the sand by the energetic action of those turbulent waters. Beds 

 of hard sandstone are so blackened by the broken fragments of coal 

 and plants, with which they are intermixed, that they cannot be used 

 for building purposes. No wonder that such mighty currents have 

 dragged with them, and buried under heaps of sand, large trunks of 

 trees, torn from the dry land of the shores, or from the forests of the 

 marshes; or that they sometimes entombed in their ponderous deposits 

 parts of forests, which are still now found standing and petrified like 

 the pillars of some old Babylon of trees. 



From this we may conclude, that the remains of vegetation found in 

 the beds of sandstone cannot show, generally speaking, their geologi- 



