NAZEING STAGE (PLEISTOCENE) 31
The "M" beds were examined in several sites and these
differed. The site which is selected as most suitable for regard-
ing as the type section is that which was named "M4", where
the following sequence was recorded :—
5. 60 cm. MARSH CLAY.
4. 280 cm. UPPER PEAT [Boreal to Atlantic] Black
fen-wood peat with birch, willow and reeds.
3. 74 cm. LOWER PEAT [Pre-Boreal to Boreal].
M4D. Peat with some sand and
gravel. 18 cm.
M4C3. Green mud with Pota-
mogeton in upper part, shells
and sedges in the lower. 21 cm.
Gravel, etc. 4 cm.
M4C2. Pale calcareous mud with
2. 96 cm. "M" BEDS birch, sedge, etc. 17 cm.
M4CT. Calcareous mud with
charophytes, shells and beetle-
elytra. 13 cm.
Lens of gravel. 12 cm.
M4B. Grey calcareous mud with
willow and birch. 11 cm.
GRAVELS Gravel iii.
1. [Late Black fibrous peat (M4A).
glacial] Gravel ii.
Thus, in the type area, the two subdivisions of the Nazeing
Stage differ :—
a. lithologically,
b. by the wider area covered by the earlier marl ("D"),
which Warren regarded as the deposit of a "mere" comparable
with the Broads of Norfolk today, but more impermanent or
perhaps seasonal,
c. by the fact that the later beds cut into and below the "D"
beds, and
d. by a difference in fossils, notably the Charophytes, which
occurred in the "M" beds in some abundance but not in the
other.
These differences will be kept in mind in order to test their
validity elsewhere in the valley.