134 THE ESSEX NATURALIST
seems clear that the Galley Hill skeleton is not 250,000 years
old, as some had maintained, but probably less than 10,000
years.
On the other hand, the Swanscombe skull found in 1935
with an Acheulian hand-axe in gravels near Galley Hill,
gave 2 per cent fluorine, thus tending to confirm its early
Paleolithic age. In the case of the Piltdown skull, the
fragments of which were found in 1908-1912, its very
primitive type led to claims of great age for the bones-
Fluorine analysis has ascertained that it is certainly not over
100,000 years old, in spite of its simian appearance; it may
represent the straggling remnants of Eoanthropus living in
an isolated community long after its fellows elsewhere had
become extinct.
Some members of the Essex Field Club may remember
attending a valuable lecture on this subject by Dr. Kenneth
Oakley, of the British Museum, two or three years ago. I
would stress the fact that the fluorine method is a relative,
and not an absolute, dating technique.
We now come to another technique with the formidable
name of Dendrochronology, which does provide an absolute
clock, although sometimes it is rather hard to read the time
by it. When the indications are unmistakable, the age of a
piece of timber is given to the nearest year—that is to say,
the year in which the outermost part of the timber was alive.
The method is confined to tree-wood and depends on
variations of the rate of growth in different years. It is
known that there are cycles of growth, which are well
exemplified in the swelling boles of royal palms, which
exhibit what architects would call entasis in a marked and
periodic manner. The fact that there are some 11 annual
scale-rings between successive periods of maximum growth
(in the case of royal palms) and about the same number of
annual rings between the times of greatest increase of
deciduous timber trees, has led to the suggestion that this
shows a correspondence with the solar energy-cycle and
sunspot maxima. This correspondence may well be real,
but it is not a necessary premise for the success of
dendrochronological method. All that is requisite is that
growth-rate should not be constant throughout the years, but