CROMER FOREST-BED. 
187 
and that a change of climate may account for the discrepancy. 
But, in reply to this, it is enough to point out that the most 
typically southern of the freshwater mollnsca occur mixed with 
the arctic marine shells in the Weybourn Crag, and that several 
of the arctic marine species occur in the Forest-bed. We may 
therefore fairly conclude that the two faunas lived in adjoining 
districts during the same period. I have laid special stress on 
the comparison of the mollusca, for we have long lists of the 
species inhabiting the land, the sea, and the lakes ; nevertheless, 
as far as known, the same discordance affects other classes. The 
land mammals have a decidedly southern facies, while the 
marine forms seem distinctly northern. The plants of the 
Forest-bed are not arctic. To explain, these contradictions, it 
will be necessary to bring forward more evidence as to the 
conditions under which the animals and plants flourished. The 
changes in physical geography since the Pliocene period have a 
very direct bearing on the question. 
The most important feature in the physical geography of the 
period was undoubtedly the large Forest-bed river. If the 
direction of the flow of the river can be traced, we have the key 
by which the general topography of the country can be made out. 
With a view to decide this question, the old river gravels have 
been carefully examined, for they must have been derived from 
the land over which the river flowed. These gravels commonly 
contain fully 40 per cent, of stones other than flint; and after a 
study of the Glacial gravels and Boulder Clay stones, it is at 
once clear that they must have come from quite different districts. 
The proportions of the different rocks in 500 stones over an inch 
in diameter obtained at Bacton was :— 
Little worn flints - - - - 141 
Pebbles of light-coloured fine-grained quartzite 125 
„ flint - - - - 101 
„ vein quartz - - - 54 
Pebbles of hard sandstone - - - 6 
„ fine-grained grit - - 5 
Angular Greensand chert - - - 4 
„ green or bluish slaty rock - - 8 
Clay-ironstone (very variable) - - 61 
Various other rocks have been obtained in smaller numbers; 
and in the following list an attempt has been made to show the 
probable age of the deposits from which the whole have been 
derived:— 
Clay-ironstone with plant remains. 
Cakes of peat, often bored by 
Pholas - - - , - 
Jet, amber, and brown coal 
Green-coated flints (common) 
Hertfordshire pudding-stone 
Silicified wood - - - 
Lower Fresh¬ 
water Bed. 
Upper Eocene ? 
Lower Eocene. 
