1850.] AUSTEN SANDS AND GRAVELS OF FARRINGDON. 477 



Terebratula*. 



sella, Sow. [Fordes, Quart. Journ. Geol. Soc. 



vol. i. p. 345.] 

 lata [latissima] , Sow. 



nuciformis, Sow Oolitic. D'Archiac. 



oblonga, 5*0^ Oolitic. Von Buch. 



truncata, Sow. (not T. Asteriana, d'Orb.) ... Oolitic (uppermost beds), Germany, 

 depressa. Sow. [Von Buch. 



subtrilobata, Lej/m. Mem. Geol. Fr. pi. 15. 



f. 7-9. 

 tamarindus. Sow. D'Orb. T. Cret. pi. 505. 



f. 5-10. 

 Moutoniana, d'Orb. [Sharpe, MSS.] 

 lentoidea, Leym. 



Emarginula. 



neocomiensis, d'Orb. Devizes. Furze Hills. Neoc. of France. Vassy. 



Belemnites. 



subquadratus, Roem Hils. 



Nautilus. 



. Compare with N. depressus, d'Orb. ... Oolitic. 



In the question which seems to be raised by the position and con- 

 tents of the Farringdon deposits, as here described, it is not so much 

 the identity of specific forms which we have to consider as the facies 

 of its fauna as a whole : between deposits which have no species in 

 common, as between the neocomian and the gault and upper green- 

 sand group, such a feature is the only one we can take as a means of 

 comparison. An agreement of this sort, when it may exist, may 

 perhaps appear to some as of no great value ; if so, this is not the 

 place to controvert such a notion : what is meant by the expression 

 is this, that a genus or genera may be subdivided into natural groups : 

 and that fossil forms often correspond with geological divisions, just 

 as we find like groups among actual forms referable to particular re- 

 gions of depth or of geographical area ; it is this grouping which 

 imparts to a fossil fauna its peculiar facies, as compared with another, 

 when the same generic forms alone are considered. The facies of the 

 liassic Ammonites consists in the preponderance of Von Buch's groups 

 of *' Arietes" and "Falciferi;" that of the cretaceous Nautili in the 

 lines of furrows which cross them transversely. The neocomian 

 ammonite {A. Nutjieldiensis, Sow.) is more nearly allied to certain 

 upper oolitic forms than to any from the gault and upper greensand ; 

 so much so, that it is constantly quoted as occurring in the Portland 

 beds ; and Mr. Morris, in his description of the Nautilus Saxbyi, 

 pointed out that it was referable to a group of which all the forms 

 were oolitic. In the same manner the neocomian species of Opis, 

 according to M. d'Orbigny, is very like certain oolitic ones ; a like 

 result is obtained with reference to the Farringdon Belemnites, Tere- 

 bratulcBy corals, and sponges. 



^ The most abundant Terebratula at Farringdon is one which presents great 

 variety of form, and which is evidently the same species quoted so often by con- 

 tinental geologists as biplicata ; it as often resembles dimidiata and perovalis of 

 Sowerby, and several neocomian forms of Leymerie and D'Orbigny, and is most 

 probably a form common to a great part of the oolitic and cretaceous series. 



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