244
THE ESSEX NATURALIST.
The non-appearance of remains of other insects may perhaps
be explained by the fact that the method of recovering seeds
and fruits reduces more fragile organisms to very small frag-
ments. I am experimenting now in the hope of finding a method
which will lead to the recovery of remains of other orders, as
Diptera, Neuroptera and Hymenoptera.
As evidence of flora and fauna accumulates, reconstruction
becomes possible. Sample No. 5 (See Appendix A, p. 247) con-
tains remains of Water-lilies, Floating Pond Weed, Nitella,
Entomostraca, Fresh-water Sponge and Plumatella. Such an
assemblage of organisms suggests that the deposit accumulated
at the bottom of a large pond.
Sample No. 6, though only 43/4 inches in thickness, shows an
interesting transition in conditions of deposition. A section is
shown in fig.. 1, and indicates a typical brown peat with birch
stems passing into mud-like material formed of finely-divided
plant remains wherein brackish-water plants (Ruppia rostellata)
and animals (cockles) are imbedded. In the diagram, brackish-
water organisms are placed on the left and fresh-water and land
organisms on the right. There is no direct evidence as to which
were the upper and which the lower layers of this deposit, but
it would seem more probable that the mud overlaid the peat; for
the mud consists of detritus derived from the peat, that disinte-
gration taking place during an inundation by the sea, most likely
during subsidence. This seems to be the most feasible explan-
ation for the association of remains of a submerged brackish-
water plant like Ruppia with those of a typical land plant, the
birch.
Shelly clay in association with Moorlog has been described by
Mr. J. W. Stather, F.G.S.,2 who suggests that the shelly clay
overlies the peat.
Despite the rich and varied harvest of organic remains yielded
by Moorlog, there is yet little evidence as to the age of the
deposit. Probably there is more than one peat bed in the
Dogger Bank, for one specimen contains sub-arctic plants, among
them, the Dwarf Birch, Betula nana. Clement Reid,3 speaking of
the relationship of the Dogger Bank deposits to similar ones in
Great Britain, says: "These questions cannot be answered con-
2 J. W. Stather. "Shelly Clay Dredged from the Dogger Bank," Quart. Journ. Geol. Soc.,
vol. lxviii., 1912, pp. 324-27.
3 Clement Reid, F.R.S., Submerged fortis, 1913, p. 47.