296 GENERAL OBSERVATIONS. 



lowest ; and there are beds between them, particularly sandstone and 

 sandy shale, containing almost none. In general, the siliceous strata 

 contain the fewest, and the calcareous and argillaceous the most ; 

 yet in the red sandstone, which is both calcareous and argillaceous, 

 we have found none. There is no doubt, that quantities of animal 

 and vegetable matter, originally imbedded in the strata, have been 

 entirely dissolved, as we find only the harder substances remaining ; 

 and these too in various states of preservation, according to the 

 quality of their matrix. 



15. The organic remains, in some of the strata, consist wholly 

 or chiefly of marine productions ; and in others, of land productions ; 

 while in most, there is a mixture of both : nor is there any thing in 

 our strata, that favours the hypothesis of an alternation of fresh-water 

 and marine formations. — The petrifactions discovered in the coal and 

 the bituminous shale, in the siliceous sandstones and some of the 

 sandy shales, have been derived from the land ; consisting of wood, 

 and other vegetable substances ; in other strata, as in the blue lime- 

 stone, we have seen only marine shells: but most beds abounding 

 with organic remains, display a promiscuous assemblage of petrifac- 

 tions of both sorts. The most natural inference to be drawn from these 

 appearances is, that when the strata were deposited, the productions 

 of the sea and the land were blended together; and that, as 

 might be expected, they were lodged in the different strata in 

 various proportions ; some beds containing most of the one kind, 

 some most of the other, some both, and some neither. Some French 

 authors, however, to whom science is otherwise much indebted, having 

 discovered among the strata over the chalk near Paris, some beds 

 containing what appeared to be fresh-water shells, alternating with 

 others containing marine productions, have accounted for this pheno- 

 menon, by supposing, that such spots have been alternately over- 

 whelmed by the sea, and by a fresh-water lake 5 a notion which has 



