400 



KELLOWAY ROCK. 



[Ch. XX. 



clay," sometimes not less than 500 feet thick. In this there are no 

 corals, but great abundance of cephalopoda, of the genera Ammonite 

 and Belemnite. (See figs. 398, 399.) In some' of the finely lami- 



Fk 



Bel&mnites hastatus. Oxford clay. 



nated clays ammonites are very perfect, although somewhat com- 

 pressed, and are frequently found with the lateral lobe expanded on 

 each side of the opening of the mouth into a single horn-like projec- 

 tion (see fig. 399). These were discovered in the cuttings of the 

 Great Western Railway, near Chippenham, in 1841', and have been 

 described by Mr. Pratt (An. Nat. Hist., Nov. 1841). 



Fig. 399. 



Ammonites (Jason, Eeinccke. Syn. A. fflizabethce, Pratt). 

 Oxford clay, Christian Malford, Wiltshire. 



Similar elongated processes have been also observed to extend from 

 the shells of some belemnites discovered by Dr. Mantell, in the same 

 clay (see fig. 400), who, by the aid of this and other specimens, has 

 been able to throw much light on the structure of this and other sin- 

 gular extinct forms of cuttle-fish.* 



Kelloway Hock. — The arenaceous limestone which passes under this 

 name is generally grouped as a member of the Oxford clay, in which 

 it forms, in the south-west of England, lenticular masses, 8 or 10 feet 

 thick, containing at Kelloway, in Wiltshire, numerous casts of am- 

 monites and other shells. But in Yorkshire this calcareo-arenaceous 

 formation thickens to about 30 feet, and constitutes the lower part of 



See Phil. Trans., 1850, p. 393 ; also Huxley, Memoirs of Geol. Survey, 1864. 



