On. XX.] 



STOXESFIELD SLATE. 



405 



removed portions have been replaced by clay." * In such shallow- 

 water beds shells of the genera Patella, Nerita, JRi?nula, and Cylindrites 

 are common (see figs. 406 to 409) ; while cephalopods are rare, and, in- 



Fig. 405. 



Fig. 404. 



Terebratula digona. 

 Nat. size. Bradford clay. 



Fig. 407. 



Purpuroidea nodulata. 



i nat. size. Great Oolite, 



Hinctrinliampton . 



Fig. 408. 



Fig. 406. 



Cylindrites acntus, Sow. 



Syn. Actceon acutus. 



Great Oolite, 



MinchiiLhampton. 



Fig. 409. 



Patella rugosa, Sow. 

 Great Oolite. 



Nerita costulata, Desh. 

 Great Oolite. 



Eirnula {Emarginula) elath- 

 rata, Sow. Great Oolite. 



stead of ammonites and belemnites, numerous genera of carnivorous 

 trachelipods appear. Out of 142 species of univalves obtained from 

 the Minchinhampton beds, Mr. Lycett found no less than 41 to be 

 carnivorous. They belong principally to the genera Buccinum, Pleuro- 

 toma, Postellaria, Murex, Purpuroidea (fig. 405), and Pusus, and ex- 

 hibit a proportion of zoophagous species not very different from that 

 which obtains in warm seas of the Recent period. These zoological 

 results are curious and unexpected, since it was imagined that we might 

 look in vain for the carnivorous trachelipods in rocks of such high anti- 

 quity as the Great Oolite, and it was a received doctrine that they did 

 not begin to appear in considerable numbers till the Eocene period, 

 when those two great families of cephalopoda, the ammonites and belem- 

 nites, had become extinct. 



Stonesfield slate. — The slate of Stonesfield has been shown by Mr. 

 Lonsdale to lie at the base of the Great Oolite.f It is a slightly oolitic 

 shelly limestone, forming large lenticular masses imbedded in sand, 

 only 6 feet thick, but very rich in organic remains. It contains some 

 pebbles of a rock very similar to itself, and which may be portions of 

 the deposit, broken up on a shore at low water or during storms, and 

 redeposited. The remains of belemnites, trigonia3, and other marine 



* Lycett, Geol. Journ., vol. iv. p. 188. 

 f Proceedings Geol. Soc, vol. i. p. 414. 



