Ch. XX.] 



LOWER OOLITE. 



305 



Fig. 363. 



^=3&i 



; 'S^M 



^ 



gl 



fe 



Belemnites Puzosicmw, 



D'Orb. 



Oxford Clay, Christian 



Malford. 



a, a. Projecting processes of 



the shell or phragmo- 

 cone. 



b, c. Broken exterior of a 



conical shell called 

 the phragmocone, 

 which is chambered 

 within, or composed 

 of a series of shallow 

 concave shells pierced 

 by a siphoncle. 



c, d. The guard or osselet, 



which is commonly 

 called the belemnite. 



Similar elongated processes have been also ob 

 served to extend from the shells of some belem- 

 nites discovered by Dr. Mantell in the same clay 

 (see fig. 363), who, by the aid of this and other 

 specimens, has been able to throw much light on 

 the structure of this singular extinct form of 

 cuttle-fish* 



Lower Oolite. 



Cornbrash and Forest Marble. — The upper 

 division of this series, which is more exten- 

 sive than the preceding or Middle Oolite, 

 is called in England the Cornbrash. It con- 

 sists of clays and calcareous sandstones, which 

 pass downwards into the Forest Marble, an 

 argillaceous limestone, abounding in marine 

 fossils. In some places, as at Bradford, this 

 limestone is replaced by a mass of clay. The 

 sandstones of the Forest Marble of Wiltshire are 

 often ripple-marked and filled with fragments of 

 broken shells and pieces of drift-wood, having 

 evidently been formed on a coast. Rippled slabs 

 of fissile oolite are used for roofing, and have 

 been traced over a broad band of country from 

 Bradford, in Wilts, to Tetbury, in Gloucestershire. 

 These calcareous tile-stones are separated from 

 each other by thin seams of clay, which have 

 been deposited upon them, and have taken their 

 form, preserving the undulating ridges and fur- 

 rows of the sand in such complete integrity, that 

 the impressions of small footsteps, apparently of 

 crabs, which walked over the soft wet sands, are 

 still visible. In the same stone the claws of 

 crabs, fragments of echini, and other signs of a 

 neighboring beach are observed.f 



Great Oolite. — Although the name of coral- 

 rag has been appropriated, as we have seen, to a 

 member of the Upper Oolite before described, 

 some portions of the Lower Oolite are equally 

 entitled in many places to be called coralline 

 limestones. Thus the Great Oolite near Bath 

 contains various corals, among which the Euno- 

 mia radiata (fig. 364 is very conspicuous, single 

 individuals forming masses several feet in diam- 



* See Phil. Trans. 1850, p. 393. 

 f P. Scrope, Geol. Proceed. March, 1831. 

 20 



