and Fresh-joater Deposits of Easter 7i Norfolk. 373 



Jge of the fresJvwater deposit. — Next, as to the age of the 

 freshwater beds, we know as yet too little of the species of 

 mammalia, fish, insects, and plants, which are imbedded in 

 them in considerable abundance, to entitle us to lay much 

 stress on their evidence alone. But we liave from Mundesley 

 and Runton, at least nineteen species of shells in an excellent 

 state of preservation, namely, Faluditia vivipara, P. iinpura, 

 P. minuta^ Valvata piscinalis, V. cristata, Limnea palustris^ 

 L. stagjialis, L. glutinosa^ L. peregra, Planot^bis vortex, P. 

 imbricatus, P. albus, P. marginatus, P. lavis. Alder, Ancylus 

 lacustris, Cyclas cornea, C. appendiculata, C. amnica, var,? 

 and C pusilla. 



Of these all but two are certainly identical with species 

 now living in Great Britain. One of these two^ Cyclas, fig. 

 11, p. 364, may possibly be a variety of our living C amnica, 

 while the other, Paludina minuta, fig. 4, p. 354, is unknown. 

 I have not included in the list the shell allied to Turbo idvce, 

 because it would be unsafe to decide on a species from a 

 single individual; nor have I enumerated among the recent 

 species Ajiodon cygneus and XJnio ovalis, although there is 

 little doubt that the freshwater mussels of Mundesley and 

 Sidestrand belong to these species. 



Upon the whole we may conclude that this freshwater de- 

 posit must agree very nearly in age with those of Stutton in 

 Suffolk, Grays in Essex, Cropthorn in Worcestershire, and 

 others, which contain nearly the same species, with fossil 

 bones of extinct quadrupeds. It is still a question in all 

 these cases, whether all the species are not living, although 

 some ^Q\\ may not be British shells, or whether there is really 

 a very slight per centage of lost species, to which opinion 1 

 incline. It will be seen that the freshwater stratum in the 

 mud cliff's everywhere overlies the crag when in contact. 

 Many, however, of the same species of fluviatile or lacustrine 

 shells are found intermixed with the marine crag itself near 

 Norwich, in which latter the same Cyclas figured above 

 (p. 364) is met with. 



Age and origin of the drift. — As to the age of the drift, it 

 is proved by direct superposition to be newernot only than 

 the Norwich crag, but also than the freshwater beds at Run- 

 ton and Sidestrand. At the same time the section at Mun- 

 desley (fig. 2, p. 353) seems to prove, that in some places 

 the deposition of the drift was going on contemporaneously 

 with the accumulation of freshwater beds. To frame a 

 satisfactory theory respecting the origin of the drift is 

 difficult. The fluvio-marine contents of the Norwich crag 

 imply the former existence of an estuary on the present 



