70 THE ESSEX NATURALIST.
The Boyn Hill and Taplow phases in the evolution of the
Essex rivers were followed by a minor glacial period, which does
not appear to have affected Essex to any notable extent. The
following Quaternary period, however, was remarkable for
the Neolithic buried channel at about—60 ft. O.D. This resulted
in an eastward extension of the coastal area of Essex, the North
Sea having become shallow and marshy. Although the later
phases of this period (probably Neolithic) cannot be dealt with
more fully here it seems proper to give some account of the
important geomorphological results that supervened.
The gradual positive sea movement that followed this so-
called Neolithic period gave rise to the broad drowned estuaries
which are characteristic of the Essex coast of to-day. (Cp.
the Crouch, Blackwater and Stour). Furthermore, the north-
western rivers of the glaciated area continued to bring down their
heavy load, which was deposited at the new strand-line by the
check given to the rivers. Continued deposition upon the old
drowned offshore river platform has resulted in the extensive
areas of silted channels and marshy saltings that have increased
during historical times. It was probably during this Neolithic
period that the Thames entered the North Sea by way of its
present channel, thus completing the existing riverine scheme of
Essex.
JELLYFISH.
THE DIFFICULTIES OF THE STUDY OF THEIR LIFE HISTORY
AND OTHER PROBLEMS.
By F. J. LAMBERT.
PERSONS idly watching Medusae floating or pulsating
in the sea, or left on the sands by the tide, usually regard
these creatures with dislike, as things belonging to another world
and outside their ken, poisonous, and to be dreaded.
As a matter of fact, of the five forms which are normally
visible around our coasts, only one Cyanea can be regarded as
injurious to human beings, and then only so far as the more
delicate parts of the body are concerned. It will be noted that
I have spoken of "Medusae," but this visible form, which is
really the only manifestation of this form of life known to the
public, is merely one metamorphosis of six passed through by our