292 ON THE PARTICULAR ORDER OF 



the attempt to refer particular beds in distant places, 

 to some favourite deposit found elsewhere, is a no 

 less frequent source of difficulty than of fallacious 

 generalization. 



The next series of the English Geologists is called 

 the green sand formation, comprising three inferior 

 groups. The first of these is known by the name of 

 the ferruginous sand ; very constant in its character and 

 position, and forming a remarkable member of the 

 whole series of the English secondary strata. It con- 

 tains masses of sandstone and beds of ochre, clay, 

 and of fullers' earth. Above this is a complicated 

 bed of clays, called the Tetsworth clay, and that 

 again is followed by another arenaceous deposit* 

 called the green sand, including some of the most 

 recent sandstones, together with limestone. 



The next and highly important series is the Chalk, 

 divided into three beds ; the lowest known by the 

 name of chalk marl, the next being pure, and the 

 third containing flints. Some Geologists however 

 arrange the chalk marl in the last group, and sub- 

 divide the chalk beds more minutely. This member 

 is sufficiently remarkable, both in its mineral cha- 

 racters and the nature of its contents, to be recog- 

 nized and compared with other similar deposits in 

 distant places ; and it accordingly offers one of the 

 most striking proofs of the very considerable extent 

 occupied by some of the secondary strata, though it 

 must nevertheless, like the greater part of these, be 

 considered a partial deposit, when compared to the 

 remainder of the Earth's surface. It is remarkable 

 that this stratum has, in some places, undergone 

 violent dislocation and changes of position ; many of 

 the beds on the southern coast of England being even 

 in a vertical position, while the fractured state of 



