289
ON THE ZONAL STRATIFICATION OF THE
EASTERN BRITISH PLIOCENES.
By ALFRED BELL.
[Read 26th November 1910. Revised February 1912.]
FROM the time that Charlesworth separated the Crags of East
Anglia into Coralline, Red, and Mammaliferous (or Norwich)
Crag, till Prestwich brought his well-known paper before the
Geological Society,1 this tripartite division held the field. Accor-
ding to the latter writer, the Coralline Crag represented eight
zones differing in nature and faunal contents ; the Red Crag
being divided by him into two parts, the lower comprising all
exposures from Walton-on-the-Naze to Butley, together with
part of the Norwich series. Further, he could see no distinction
in the organic remains from the base to the top of this division.
Principally on these grounds, my brother (R. G. Bell) and
myself, who since 1863 or 1864 had been collecting and collating
the fauna incidental to the different pits in the Crag area, at
once expressed our dissent from these views2, our work in the
field and at home showing them to be untenable, if all the
facts were taken into consideration. We held that over the
whole area occupied by the Coralline Crag the zonification pro-
posed was not persistent (see postea) and that the fauna of the
Red Crag series, so far from being alike from bottom to top,
varied considerably ; the older portion, our Middle Crag, being
distinguished by its derivative forms, and our Upper Crag by
their absence ; as also of the phosphatic nodules and other
extraneous matter found with them, and by the replacement
of many of the true denizens of the earlier sea by others of
boreal and still existent forms.
In 1874, the late Mr. S. V. Wood, in the Supplement to the
Monograph of the Crag Mollusca, separated the Red Crag into
two zones also, but not on our lines ; and in 1890 Mr. Clement
Reid in his Survey Memoir, On the Pliocene Deposits of Britain,
summed up all that had been written on the Crag up to that time.
Some little time afterwards, Mr. F. W. Harmer, after a
long and critical examination of the subject, both at home
and on the Continent, brought his views at considerable length
on the classification, or zonal stratification, of the Crag deposits,
1 "On the Structure of the Crag Beds," etc., Quart. Journ. Geol. Soc., 1871.
2 "The English Crag.'' etc., Proc. Geol. Assoc., vol. ii, 187. A. and R. Bell. Also "The
Succession of the Crag," Geological Magazine, vol. ix., 1872. A. Bell.