290 ON THE ZONAL STRATIFICATION OF THE
as well as the conditions under which they may have originated,
before the Geological Society3, slightly modified at a little later
period.
In this sketch, I adopt Mr. Harmer's views to a large extent,
with such interpolation as I venture to hope a long acquaintance
with the Crags and their contents may justify me in proposing.
It is needless to say that the progress of knowledge requires
frequently a modification of one's earlier ideas, as new facts are
brought to light.
Since this paper was read it has been found requisite, in
order to bring it up to date, to slightly recast it, so much
fresh knowledge having accrued in the interval.
The scanty relics of the earliest Pliocene beds in East
Britain consist of ferruginous sand and sandstones occurring
in scattered patches and pipes in the underlying Chalk, extending
from the high downs near Guildford to the sea cliffs near Folke-
stone, re-appearing across the Channel on the hill tops in the
Pays de Calais and thence to Belgian-Flanders, where they
connect themselves with the ferruginous sands of Louvain and
Diest.
Throughout all this region, as far as England is concerned,
fossils only occur in two places, viz., at Netley Heath, near New-
lands Corner, Guildford, 628 feet O.D., where a few indeterminate
casts have been found, and at Lenham, 500—625 feet O.D., near
Maidstone, from whence Mr. Reid records 63 species of Mollusca.
Of these only 31 are represented in the 130 or more present in
the Diestien deposits of Belgium mentioned by him.
Several of these Lenham shells indicate an earlier date than
that of any other English Pliocene deposit, as Conus dujardini,
Pleurotoma jouanetti, Pl. consobrina, Terebra acuminata and
Area diluvii are characteristic late Miocene shells, and are not
known in the later Crag beds. The contents of the later Crag
deposits may be classed into exotics and natives. The exotics,
derived from many quarters and formations, have given rise to
3 "The Pliocene deposits of Holland," Quart. Journ. Geol. Soc., vol. lii. (1896), p. 748.
"The Lenham beds and the Coralline Crag," ibid., vol. liv. (1898), p. 308.
"The Crag of Essex, Waltonian," ibid., vol. vii., (1900), p. 705.
"The later Tertiary History of East Anglia." Proc. Geol. Assoc., vol xvil. (1902), 416.
"The Pliocene deposits of the Eastern Counties of England," Geol. Assoc. Jubilee Vol.
1908), p. 86.