Skeleton lately found at the Tilbury Docks, Essex. 139
generally noticed was the offensive smell of sulphuretted
hydrogen proceeding from the plant-remains in this bed,
though twenty feet or more below the surface. The preserva-
tion of these plants in this slightly decomposed state is of
course due to the thick clay beds, both above and below,
which have prevented total decay. These beds are simply
inundation mud, but their combination with the peaty beds
is noteworthy, as it points to periods of subsidence divided by
stationary intervals. For the reeds and other plants, the
remains of which make up the two peaty beds seen, could not
have grown below high-water mark, though the base of the
lower of the two beds is now from 20 to 25 feet beneath the
surface. The deposit of blue clay above this bed marks a
period of subsidence, then the upper peaty bed implies a
stationary interval, with a growth of vegetation about or
slightly above high-water mark. The blue clay above the
upper peaty bed points, of course, to a renewal of the
subsidence.
It will have been noticed that, in treating of the evidence
of the peaty beds as showing subsidence, I have not men-
tioned the third and still lower peaty bed, ascertained to exist,
here and there, from trial-borings and the Tilbury Fort Well,
though not visible on the day of our excursion. But this bed
is generally found to rest directly on the sand or gravel, and
its composition shows that it probably had an origin different
from those of the two others. Instead of consisting of plants
that once grew slightly above ordinary high-water mark, it is
composed of logs of wood and other vegetable matter that has
drifted down the channel and been deposited where the
current was sluggish, as it is sure to be on one side of an
island in the stream. Capt. Hall (quoted in Lyell's 'Prin-
ciples ') remarks of the islands of the Mississippi that the
interval between them and the shore is often found to be
"filled up by myriads of logs cemented together by mud and
rubbish." And as this lowest peaty bed has probably been
formed in this way, it can offer no evidence of subsidence.
No reader of the paper by Prof. W. J. Sollas, "On the
Estuaries of the Severn and its Tributaries,"4 can fail to
4 Quarterly Journ. Geol. Soc., November, 1883.