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PEOCEE DINGS OF THE GEOLOGICAL SOCIETY. 



[Apr. 24, 



1. On the Occurrence of the Cyeena eleminalis, together with Maeine 

 Shells of Eecent Species, in Beds of Sand and Geatee over beds 

 o/Boeldee-clay near Hell ; with an Account of some Boeings and 

 Well-sections in the same District. By Joseph Peestwich, 

 Esq., F.B.S., Teeas.G.S., &c. 



Few fossils of its class can lay claim to the interest that has at- 

 tached to the Cyrena jiummalis. This small hivalve shell, described 

 in 1834 by Mr. Searles Wood as the Cyrena trigonula of the 

 Norwich Crag, and afterwards identified with the C. consobrina of 

 Cailland, now living in the Nile and parts of Asia*, has, from the cir- 

 cumstance of its occurrence in beds of well-defined position beneath 

 the Boulder-clay of Norfolk, been ranked as pre-eminently a prse- 

 glacial shell, and as the associate of the Hippopotamus major and 

 Elephas antiquus. 



On the strength of the palseontological argument, certain isolated 

 beds containing the same Cyrena, including more especially the well- 

 known deposits of the Thames Yalley, the immediate relation of 

 which to the Boulder-clay is not apparent, were referred to the same 

 prseglacial period. The late Mr. Trimmer, Mr. Morris, and myself 

 hare, however, always held a different opinion, inclining to the belief 

 that these latter deposits were of later date than the Boulder-clay. 

 Our reasons being mainlybased upon the general physical phenomena, 

 and wanting the more positive proof of superposition, the age of these 

 deposits remained a point at issue between geologists and palaeonto- 

 logists. But if the determination of age were already desirable on 

 the abstract geological question, it is now of much more importance 

 in consequence of the circumstance of the same Cyrena having lately 

 been found in the neighbourhood of Abbeville in the beds of sand 

 and gravel containing Flint Implements +. 



So much of the paloeontological argument as hinges on the occur- 

 rence of the Elephas antiquus in these beds has lost its weight, inas- 

 much as this species, instead of occurring invariably in beds beneath 

 those containing the Elephas primigenius and always apart from it, 

 has now been found associated with it in positions which leave little 

 doubt of their original contemporaneity. The E. antiquus may have 

 lived before the E. primigenius ; but it certainly appears to have lived 

 on to the period of the latter species, which, the evidence I have 

 collected goes to show, was probably not introduced into this country 

 until after the Boulder-clay period. 



The Cyrena, although found in various beds supposed to be newer 

 than the Boulder-clay, could not be proved in any of these cases to 

 be newer by direct superposition. In the course of last summer, 

 however, I obtained proof of its presence in beds considerably higher, 

 at all events, than the Maninialiferous or Norwich Crag. I had visited 



* See the account given of the range of the living shell, by Mr. Woodward, 

 in the Zool. Proe. 1850, p. 187. 



t The first Cyrena found there I took out of a bed of sand overlying a bed of 

 subangular flints, in which I at the same time found three flint flakes or knives : 

 larger lance-head-shaped flint implements have been found in a still lower bed 

 of gravel adjoining the town-walls. Four more specimens of the Cyrena have 

 since been found in some sands. (See section in the Phil. Trans, for I860, p. 284.) 



