SUCCESSION AMONG ROCKS. 291 



longing to the lias. On the respective values of opi- 

 nions of this nature, it would be needless to attempt 

 a decision, were it possible. 



The remaining strata then, proceeding upwards, in 

 the lower division of what is called the oolithe for- 

 mation, are a sand of various characters, a coarse, 

 somewhat oolithic limestone, a stratum of clay some- 

 times including fullers' earth, and a limestone called 

 the Gray oolithe. The middle division contains, in 

 the same order, a calcareous and a siliceous slaty 

 rock intermixed with sand, shale, and some coal, 

 three limestones, supposed distinct, and called forest 

 marble, cornbrash limestone, and Kelloway rock, 

 and a clay called Oxford clay, or fen clay. In the 

 last, or uppermost, division, are comprised a cal- 

 careous sandstone, a limestone called Coral rag, 

 another limestone, called the upper oolithe, a clay 

 called Kimmeridge clay, a third limestone called 

 Portland stone, and, lastly, the Purbeck inferior 

 group ; consisting of limestone, shale, and marl. 



It is by no means clear that the arrangement of 

 these is so regular and constant, and the different 

 beds of so much importance, as to require the decisive 

 names which have thus been conferred on them. 

 There also appears much that is purely arbitrary in 

 those arrangements into the minor series whence these 

 characteristic terms are derived ; since, in one of 

 these artificial groups, the same substances exist as 

 are found in another part of the principal deposit, 

 forming or entering into another series. Some of 

 these deposits, indeed, seem to be as irregular in 

 their disposition as the strata of the coal series, which, 

 in their general characters they so much resemble ; 

 nor does it seem as yet possible to reduce them into 

 a system in which all observers shall agree; while 



