Both the quartzose sand, of which it chiefly consists, and the
included shells, are most commonly distinguished by a deep ferruginous or
ochreous colour, whence its name. The shells are often rolled, sometimes
comminuted, and the beds have much the appearance of having been shifting sand-
banks, like those now forming on the Dogger-bank, in the sea, sixty miles east
of the coast of Northumberland. Cross stratification is almost always present,
the planes of the strata being sometimes directed towards one point of the
compass, sometimes to the opposite, in beds immediately overlying. That such a
structure is not deceptive or due to any subsequent concretionary rearrangement
of particles, or to mere bands of colour produced by the iron, is proved by each
bed being made up of flat pieces of shell which lie parallel to the planes of
the smaller strata.
(FIGURE 122. Purpura tetragona, Sowerby; natural size.)
(FIGURE 123. Voluta Lamberti, Sowerby. Variety characteristic of Suffolk Crag.
Pliocene.)
(FIGURE 124. Voluta Lamberti, young individual, Cor. and Red Crag.)
It has long been suspected that the different patches of Red Crag are not all of
the same age, although their chronological relation can not be decided by
superposition.
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