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Clay-with-flints to a depth sometimes of fifteen feet, a formation 
which may have derived portions of its argillaceous material from 
wrecks of Tertiary beds that once overspread the area. 
It is then highly probable, that whilst so much of Norfolk 
remained as a land-area in later Eocene and Miocene times, 
extensive sheets of loose flints, mixed with earthy matter, would be 
formed on the surface. And although there is no reason to suppose 
that any formations of this early and middle Tertiary age have been 
left for our contemplation in the county, yet the materials then 
accumulated may have been ready to hand for agents in later times 
to re-assort and deposit elsewhere, if not in the same neighbourhood. 
Passing on to the Pliocene period, we come more closely to the 
border-line between things past and things present. The deposits 
of this age, which for the most part lie concealed beneath a covering 
of Drift Gravels and Boulder Clay, are exposed to our view at the 
foot of our cliffs and on the borders of the Bure and the Yare. 
They consist of pebbly gravel, sand, and “jambs” of clay, with 
here and there beds full of fossil shells called “ Crag,” that delight 
the eye of the collector. Our Norwich Crag is truly a sort of raised 
bed of the German Ocean, having been deposited at a time when 
the eastern portion of our county came within the inttuence of the 
sea. Chalk cliffs then formed its western, and for a time its 
northern boundary, and to their gradual destruction wo owe the 
flint shingle which is such an important feature in the beds. 
The Crag itself, however, exercises little influence on the scenery : 
it is only as a sub-soil, on the borders of our river valleys, that it 
gives a character to the vegetation. Of its fossil forms, many of 
the Mollusca are now living on our coasts — we find the same 
Periwinkles and Purples, the same Cockles, Pectens, and Mussels ; 
while the rivers bore down some of the same species of land and 
freshwater Mollusca. Nevertheless many forms found in the Crag 
were different from those now existing in this country, and notably 
the mammalia. Two species of Elephant, the Hippopotamus, 
Ilycena, and Mastodon, mark the great distinction in the land fauna. 
As time went on the Mastodon became extinct in the area, and the 
physical conditions of the eastern and north-eastern part of Norfolk 
became estuarine instead of marine. Bemnants of the forest growth 
of this time are preserved to us in the stools of trees, embedded in 
the gravel and silt of later Pliocene times along the Cromer coast. 
