NODULE BEDS. 
15 
of the one should differ materially from that of the other, though 
we might expect to find the'same species in different proportions, 
according to the known life-succession in Pliocene time. The older 
deposits should contain abundance of the southern species, while 
the newer should afford evidence of a preponderance of individuals 
belonging to more northern forms. In actual fact this pre¬ 
ponderance is well shown by the mollusca of the box-stones. 
Besides the cetacea the Nodule Bed contains a Walrus, Trichechus 
Huxley which occurs also in the Cromer Forest-bed. 
The land mammals, as far as yet determined, are species found 
in Pliocene strata on the continent—such as Mastodon arvernensis 
(Fig. 2)—with the addition of a few still unknown except in the 
Pig. 2. 
Mastodon arvernensis, Or, & Job. 
Half natural size. 
a. Side view of tooth, b. Grinding surface of same specimen. 
Nodule Bed ; none are exclusively Miocene. No land mammals 
having yet been discovered in the Coralline Crag or in the Diestian 
of Antwerp, we must guard against concluding from a comparison 
of the mammalian fauna of the Nodule Bed with that of the Forest- 
bed that they cannot both be Pliocene, for in this country most 
of the intervening links in the chain are missing. In the Appendix 
is given a complete list of the vertebrata from the Nodule Bed, 
but it may be observed that two or three of the species may 
possibly belong to the period of the Bed Crag, of which deposit 
the Nodule Bed is merely the conglomeratic base. 
Pits for coprolite,” or phosphatic nodules have constantly been 
alluded to in the previous pages. The raising of this material 
