14 
NODULE BEDS. 
may not be contemporaneous with the shells, though the majority 
are undoubtedly derived from the underlying London Clay. A 
tooth of Carcharodon megalodon (Fig. 1) has been found imbedded 
Fig. 1. 
Carcharodon megalodon^ Ag. 
Half natural size. 
(From a specimen retaining traces of the characteristic serrated margin, in the 
Museum of Practical Geology.) 
in the box-stone matrix, and has been quoted as an indigenous 
fossil; other specimens of the same species may be of much older 
date, and even the specimen in a box-stone may have been 
originally washed out of an older deposit. 
The mammals, having a more restricted range in time, are 
more easy to deal with, for we can at once put on one side 
Corgpliodon and Hyracotherium as undoubtedly derived from 
Eocene strata. The other species from the Nodule Bed fall 
naturally into two groups—the cetacea and seals, and the land 
mammals. These are divided into several groups by Professor 
Ray Lankester, who is inclined to treat them as derived from 
various deposits of Miocene and Pliocene age, but I do not think 
there is any reason to consider that this derivative fauna belongs 
to more than two periods—the Lower Eocene and the Older 
Pliocene. The marine mammals, as far as yet determined, seem 
to correspond with those of the Diestian Sands of Antwerp.* 
The Diestian Sands and the box-stones are probably, however, 
so nearly of the same age, that there is no reason why the fauna 
* There seems still to be some uncertainty as to the exact horizon from which 
many of the Antwerp cetacea have been obtained. 
