28 Succession 



from west to east across the Secondary and Tertiary 

 strata, and examine the fossils found in successive forma- 

 tions, we discover that they are not the same in all, and 

 that most of them contain marine organic remains, 

 which are in each formation of species and sometimes of 

 genera more or less distinct from those in the forma- 

 tions immediately above or below. 1 



Thus turning again to fig. 5, p. 25, the Ked Marly 

 series No. 1, is rarely fossiliferous, and such fossils as 

 these beds may contain are chiefly land plants, footprints 

 of Amphibia, and small bivalve crustaceans. The 

 Khaetic beds 2, contain sea-shells of a few genera and 

 species, the latter somewhat distinct from those found 

 in the Lower Lias No. 3, the fossils of which are again 

 partly, but not altogether, of different species from those 

 buried in the Marlstone No. 4, which again partly 

 differ from the forms in the Upper Lias clay No. 5, and 

 so on, stage by stage, through the remaining strata of 

 the Oolitic rocks, up to the Kimeridge Clay No. 11. 

 Throughout the whole series from the Ehaetic beds (2), 

 upwards to the Kimeridge Clay (11), there is an inti- 

 mate relation, for in all the Liassic and Oolitic forma- 

 tions the general facies, that is to say, the grouping of 

 genera (Ammonites, Belemnites, Terebratulse, Phola- 

 domyas, Oysters, &c.) is the same, and some species 

 generally pass from each formation into the next above 

 it; and not only so, but sometimes through several 

 formations. There is, however, generally enough of 

 difference in the species found in the different forma- 

 tions to enable anyone with sufficient knowledge to tell 

 by fossils alone, if he found enough of them, what 

 formation he may chance to be examining. When, 



1 There are also a few freshwater deposits, but the discussion of 

 these is not essential to the present argument. 



