340 



J. P. BLAKE AND W. H. HUDLESTON ON 



Fossils of the Upper Calcareous Grit, Pickering. 



r. Belemnites nitidus, Bollf. 



c. Ammonites, sp.(cf.Acliilles,Z>' (>&.). 



o, " biplex." 



alternans, Von Buch. 



Chemnitzia, sp. 



Patella rnosensis, Buvig. 



Exogyra nana, Sow. 

 c. Oslrea bullata, Sow. (Oyster- 

 bed above " throstler "). 



Avicula ovalis, Phil., var. obliqua. 



Perna mytiloides, Lam. 

 c. Pecten midas, B'Orb. 



demissus, Phil. 



v.c. 



c. 

 c. 



Modiola cancellata, Rom. (dwarf). 

 Trigonia Voltzii, Ag. 

 Protocardium, small sp. 

 Lncina aspera, Buvig. 



substriata, Rom. 



? Corbicella. 



Groniomya literata, Sow. 



v-scripta, Sow. 



Pleuromya tellina, Ag. 

 — — Voltzii, Ag. 

 Myacites &c. (numerous). 

 Thracia, sp. (of. clepressa, Sow.). 

 Discina elevata, Blake. 



The section at Pickering is so complete, so accessible, and so easy 

 to trace, that we may be pardoned for having dwelt upon it at con- 

 siderable length. The divisions adopted might, perhaps, in some 

 instances, be considered slightly arbitrary ; but there are, without 

 doubt, three principal divisions or groups, corresponding to (1) The 

 upper part of the Middle Calcareous Grit, here in unusual force, (2) 

 The Upper Limestones, i. e. the Coralline oolite and the equivalents 

 of the Coral Rag, and (3) The Upper Calcareous Grit. Of these the 

 former two are blended by passage-beds, whilst the latter is sharply 

 separated from the middle member. The absence, as far as 

 Ave know, of Ammonites per armatus, even from the lowest quarries, 

 proves that we are dealing with a different fauna from that of the 

 Lower Calcareous Grit, as does also the absence of Rhynchonella 

 Thurmanni, so characteristic of that horizon and of certain portions 

 of the Lower Limestones ; so that, if we did not know it on strati- 

 graphical grounds, we might suspect that the " freestones " of Pick- 

 ering could scarcely belong to the Lower Calcareous Grit proper. 

 Still the abundance of cordate Ammonites in the lowest accessible 

 portions shows that we have not yet done with the Oxfordian fauna. 



Throughout the whole series, from the Trigonia-heda well into the 

 Coralline oolite, Ammonites generally referable to A. plicatilis are 

 obtained ; these sometimes attain enormous dimensions. "We would 

 draw attention again to the abundance of corals in the base of 

 group g, unassociatcd with the Rag-urchins, which, with the Mya- 

 cidoe and Anatinidse seem, throughout the section, to be wanting. 



The principal limestones, group/, from their usually compact nature, 

 with only an occasional mixture of oolite, seem to have been the result 

 of finely ground coral-mud, which has produced these calcareous pastes 

 with oolitic grains, in some cases so closely cementing the shells and 

 other organic fragments as to form rocks with a fracture almost like flint. 

 The physical history of such beds, whether compact or oolitic, seems 

 to have been this : — The coral is being perpetually ground down to 

 the finest powder, which is held suspended in the sea like ordinary 

 sediment ; but as it falls towards the bottom, it encounters an acid 

 stratum of water, due to the quantity of carbonic acid generated by 

 the decomposition of organic matter and the respiration of animals. 

 This slightly attacks the calcareous sediment and forms the usual 



