and Freshwater Deposits of Eastern Norfolh 373 
Age of the freshwater 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 have from Mundesley 
and Runton, at least nineteen species of shells in an excellent 
state of preservation, namely, Faliidina vivipara^ P. impura, 
P. minuta^ Valvata piscinalis^ V. cristata, Limnea patustris, 
L. stagnalis, L. glutinosa, E, peregra^ Planorbis vortex^ P. 
imbricatus, P. albus^ P. marginatus, P. Icevis^ Alder, Ancylus 
lacustrisy 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. 
1 1, 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 ulvre, 
because it would be unsafe to decide on a species from a 
single individual ; nor have I enumerated among the recent 
species Anodon cygneus and U7iio 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 few may not be British shells, or whether there is really 
a very slight per centage of lost species, to which opinion I 
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 
