152 
CROMER FOREST-BED. 
Lower and the Upper Freshwater Beds were laid down. Certain 
species are doubtless known at present from one division only, 
but this partial distribution seems more probably to indicate 
mere local circumstances than any great lapse of time. Leaves 
of the elm and the beech, for instance, have only been found at 
the base of the Forest-bed Series and at one locality ; these 
trees, however, are species generally characteristic of dry soil, and 
their leaves therefore could scarcely be expected to occur except 
merely locally in such deposits as those of the Forest-bed. On 
the other hand the hornbeam, maple, and hawthorn are only" 
indicated by fruit, found abundantly in the Upper Freshwater 
Bed at one locality, but rare or entirely absent elsewhere. Many 
of the mammals also at first sight would seem to be confined to 
certain portions of the series ; but this local distribution on 
further inquiry resolves itself into a separation of the la,rge 
species from the small. Elephant and hippopotamus remains, for 
example, are almost confined to the estuarine and fluviatile 
gravels ; voles and shrews are abundant in the Upper Fresh¬ 
water Bed, but extremely rare below. The Lower Freshwater 
Bed seldom yields bones of any sort, for peat and peaty clays, 
such as are usually found on this horizon, are unfavourable to 
the preservation of osseous remains. 
From the examples, just brought forward, of the partial dis¬ 
tribution of the fossils, it will be understood that negative 
evidence is of doubtful value when an attempt is made to fix 
the limits in time of any one species. The elephants, or the 
elm and the beech, may well have ranged throughout the Forest- 
bed Series, though up to the present time traces of them may 
only have been found on one horizon. Each year additional 
species, formerly known from one division only, are found to 
range into others, and the difference between the various hori¬ 
zons, which in the Cromer Memoir was somewhat emphasised, 
is in this volume considered to be of less value than the links 
which bind the strata together into one set of estuarine, fluviatile, 
and lacustrine deposits. 
It must not be thought—notwithstanding what has just been 
said—that the careful separation of the fossils of each zone is a 
matter of no importance, for unless this separation is made we 
shall never be able to understand, or take into account, the 
successive waves of migration which must have passed over the 
country in Pliocene times as they do in the present day. The 
above remarks are merely intended to prevent any reliance being 
placed on negative evidence, in the present imperfect state of 
our knowledge of Pliocene natural history. The complicated 
details relating to local distribution, and to the various deposits 
in which the species occur, could not be given in this Memoir 
without making it far too bulky. A considerable proportion of 
these details has already been given in the Cromer Memoir; the 
remainder is preserved in manuscript in the Office of the Geolo¬ 
gical Survey. 
