They form
patches rarely exceeding twenty feet in thickness, resting on white chalk. At
their junction with the chalk there invariably intervenes a bed called the
"Stone-bed," composed of unrolled chalk-flints, commonly of large size, mingled
with the remains of a land fauna comprising Mastodon arvernensis, Elephas
meridionalis, and an extinct species of deer. The mastodon, which is a species
characteristic of the Pliocene strata of Italy and France, is the most abundant
fossil, and one not found in the Cromer forest before mentioned. When these
flints, probably long exposed in the atmosphere, became submerged, they were
covered with barnacles, and the surface of the chalk became perforated by the
Pholas crispata, each fossil shell still remaining at the bottom of its
cylindrical cavity, now filled up with loose sand from the incumbent crag. This
species of Pholas still exists, and drills the rocks between high and low water
on the British coast. The name of "Fluvio-marine" has often been given to this
formation, as no less than twenty species of land and fresh-water shells have
been found in it.
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