from the Characters of their embedded Fossils. 237 



Mr. W. Richardson, also, has described (Mag. Nat. Hist., 

 vol. i. p. 122. n. s.) the manner in which bones and shells 

 are daily removed from the gravel and London clay of Kent, 

 and deposited in the estuary of the Thames. Most geologists 

 must have had opportunities of witnessing the same pheno- 

 menon. Among instances which have come under my own 

 observation, may be mentioned the highly interesting, though 

 little known, sponge-bed of Farringdon. This deposit, which 

 has many analogies to the coralline crag, is supposed to be 

 of the age of the green-sand. It is a thick bed of sand and 

 fine gravel resting on hills of coral rag. It contains multi- 

 tudes of beautiful sponges and other Zoophyta ; also various 

 shells, especially Terebratulae, which are commonly empty, 

 and exhibit the curious bony apparatus of the inside in a rare 

 state of perfection. Along with these delicate and beautiful 

 fossils are rolled fragments of Belemnites, and other remains, 

 which, to all appearance, are derived from the subjacent coral 

 rag. 



I lately saw a remarkable instance of the same kind in the 

 cabinet of M. Nicolet, at Chauxdefond, near Neufchatel. 

 Most of the valleys in that part of Switzerland are partly 

 filled with molasse, a Miocene deposit, containing O'streae, 

 Pectines, and various tertiary shells. Intermixed with these, 

 occur numerous secondary fossils, such as Ammonites, Be- 

 lemnites, Trigoniae, Terebratulae, &c, derived from the sur- 

 rounding hills, which correspond to the English series from 

 the Oxford clay to the chalk inclusive. 



Superficial gravel, or ancient alluvium, exhibits the same 

 intermixture of fossils of widely different epochs. In the 

 gravel of Worcestershire may be found corals from the Si- 

 lurian rocks, plants from the coal, Gryphites from the lias, 

 Terebratulae from the oolite, and Spatangi from the chalk, 

 mixed with bones of the rhinoceros and hippopotamus, and 

 freshwater shells of existing species. 



On a review of these facts, a person not conversant with 

 geology might exclaim, " How vain, then, must be the attempt 

 to class formations by their organic remains, and how gra- 

 tuitous the assumption that the fossils of any stratum are 

 contemporaneous with its deposition ! " This, however, would 

 be jumping too fast to a conclusion; and the following consi- 

 derations will show that, though geologists should always be 

 on their guard against errors arising from the intermixture 

 of fossils of different ages in the same stratum, yet the possi- 

 bility of these errors is so rare, as not to affect the general 

 deductions of geology. 



In the first place, an aqueous action of considerable vio- 



