A BRIEF SKETCH OF
THE CRAG FORMATION
OF EAST ANGLIA.
By W. H. DALTON, F.G.S. (Formerly of H.M. Geological Survey.)
THE word "Crag" is a local term used in East Anglia for
fine gravel and sand, suitable for footpaths, &c, and has
long been appropriated by geologists in a technical sense to
designate certain deposits of definite age in Essex, Suffolk, and
Norfolk.
It is practically a synonym of the word Pliocene, which
means " mostly common." as the greater part of the fossils of the
series are of species still living in British or other seas. The
Pliocene period is separated from that in which we live, only by
the Glacial epoch, although the term Postglacial is often used in
a restricted sense, excluding the most recent times.
The Crag series consists of two divisions, separated by an
interval of time not represented by any deposit, but marked, on
the contrary, by partial destruction of the earlier portion of the
series, as will be described in the account of the newer division.
It is needless to enter here into the questions of the exact
proportion of living to extinct species, of the distribution in
warmer and colder climates, or in Continental deposits, earlier,
coeval or later, such as occur in Belgium, Italy, and elsewhere.
These numerical details vary with every fresh discovery, and
with individual differences of opinion as to identity of species, but
a still stronger reason for avoiding such discussion lies in the
fact that in such current-piled banks shells that have been trans-
ported for some distance, and others that have been derived from
older beds, are mingled with those living on or close by the place
of deposit. Also, the lists published seldom distinguish between
rare and common forms. Mr. F. W. Harmer, a veteran Crag
geologist, wrote in 1898, that
" To attach the same importance, for the purpose of analysis, to a
species of which a single specimen, or at the most a very few, may have
been discovered as the result of the labours of nearly a century, as to