EASTERN BRITISH PLIOCENES.
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a pre-Crag workshop or "floor," subsequently covered by the
waters of the incoming Crag-sea, bringing with it the detritus
of the removed strata and London Clay to be mixed with the
stones and flints, and as their level rose still higher, picking up
teeth and bones off the sinking land and the harder woods-
Palms, Conifers and Angiospermous Dicotyledons. The worked
stones have not been found below the older Gedgravian
zone. In the only nodule-bed exposed below the Coralline
Crag at Sutton, which was closed 50 years ago, unworn flints
are alone mentioned, but they may not have been noticed.
The Crags proper commence with the lower or Coralline Crag
(the Gedgravian of Mr. Harmer), the main mass centring about
Sudbourne, extending northwards to Aldborough, with a few
outliers off Sizewell, Sutton and Tattingstone. The lower of the
two divisions of Prestwich consists of light coloured sand with
many fossils, and an upper one, or Bryozoan Crag, indurated
into a more or less compact rock. Mr. Harmer considers these
beds originated as sub-marine banks of drifted material, brought
together by tidal action under influence of S.W. currents in a
sea of moderate depth.
The floor or bottom silt exhibits some of the soft sand-loving
bivalves, such as Mya and Panopaea, in their normal position.
Double bivalves abound, but the bulk of these occur in
separated valves. The molluscs seem to be slightly gregarious,
the larger forms occurring in one horizon, the smaller in another.
This may be due to the sifting of the fossils by current action.
This does not seem to have been very strong, as the shells are
seldom, if ever, rolled or worn, and permitted the growth of large
masses of the ramose and foliaceous Polyzoa, such as Sali-
comana and Eschara. The upper portion consists of a soft
consolidated mass of comminuted remains of all kinds, often
deeply stained. Such shells as were composed mainly of ara-
gonite are nearly all destroyed by the infiltration of acidulated
waters, leaving beautiful moulds of the interior, but those built
of calcite, especially Pectens, are well preserved, often covered
with well preserved adnate Polyzoa. These appear to have
been drifted. Crabs of many species are plentiful. A fine and
unique specimen of the Common Lobster, and one of a large
Echinoid new to Britain (Clypeaster marginata) is now in the
Moot Hall, Aldborough. It seems worth notice that while