PALiEONTO LOGIC AL REPORT OF GEOLOGICAL SURVEY. 521 



cal level. Beds of sandstone appear, particularly marked with the 

 remains of broken plants. It may be that by a mighty cataclysm, 

 immense marshes, covered with trees, have been entirely swept over, 

 and that their remains, bruised and ground by a prolonged action of the 

 waves, have eventually been carried and deposited over the whole area 

 of the basin. It may be, also, that the large trunks, either standing 

 or heaped up together, in some parts of the coal-fields, where they are 

 found now in great abundance, bear evidence of a general and remarka- 

 ble cataclysm; and that they may thus indicate a constant geological lev- 

 el in their position. Some incomplete observations tend to confirm this 

 supposition, but they are still too scanty, and need to be pursued over 

 a wide area. 



It is scarcely necessary to explain why, in the beds of sandstone, 

 the trunks of trees are mostly petrified, preserving their general out- 

 line, and not flattened as in the coal. Not only the sand is too porous 

 a matter to prevent entirely the access of the air, but its mineral ele- 

 ments have exerted a constant action on the woody matter, and des- 

 troyed it entirely, or taken its place, leaving only its outline carved 

 like a mould in, the stone. Or they have transformed it to some 

 stony substance — -either silex or carbonate of lime and spar — preserv- 

 ing thus partially, not only the external features, but even the internal 

 structure of the wood, to the most delicate fibres and vessels. 



It has been asked many times, why, siuce the sandstone is a narine 

 formation, it does not contain any shells, any remains of marine aui- 

 mals 1 Indeed, this question would be unanswerable if we were to 

 suppose that the materials carried by the sea had formed its bottom,. 

 This supposition is not inadmissible. Though the depression of an imi 

 mense plain near the sea shores would take it below the level of the 

 water, it could not raise the bottom of the sea, and spread its sand, 

 over it. But every one knows that the sea shores are every where 

 bordered by hills of sand, sometimes several hundred feet high, and, 

 extening many miles, like huge inland waves. Near the mouth of 

 the Elbe and of the Rhine, those hills penetrate the country for hun- 

 dreds of miles. The sand of which they are composed — coarse or 

 fine — is sometimes mixed with gravel 3 but contains no shells or ani? 

 mal remains. Such sand hills have probably furnished the materials 

 for the sandstones of the Coal Measures; at least this is to me the only 



satisfactory explanation of their formation and composition. 

 66 



