CONCERNING THE AGE OF THINGS 131
remains of paleolithic man, the age of the formations can
now be given with some confidence to within perhaps 20-30
per cent. In some favourable situations, the rate of
accretion by the deposition of dust seems to have remained
constant for tens or even hundreds of thousands of years,
and this rate of change of surface level provides the external
clock in such cases. But in many—indeed, in most—parts
of the world there can be no such assumption of steady
change, and then the only help which the older techniques
can provide comes from a study of comparative geology, the
known correspondence between similar strata all over the
face of the world, and the fossil remains which they contain.
A great corpus of paleobotanical and paleontological
knowledge has now been built up, and the sequence of
development of many forms of living things is known, with
a rough approximation to a time-scale in some cases.
Provided one can be sure that the object to be dated is really
contemporary with a known stage of one of the well-studied
evolutionary series, it may be possible to determine the age
of the object by inference.
The most recent contribution from paleobotany is the
pollen distribution in ancient times; the subjoined table
shows, for example, the trend of pollen prevalence in
Northern Europe during the past ten thousand years, but
the information of pollen distribution is more extensive and
not limited to the species of trees given in the table, or to
the periods shown :—
Table 1
Dating by Pollen Analysis
Approximate Time
Prevalent Pollen-producing in Years
Trees Before the Present
Alder, Elm, Oak, Lime ...... 4,500 to 7,000
Pine, and some Alder, Oak, Lime, Elm 7,000 to 8,750
Willow, Pine, Birch ......... 8,750 to 10,250
(In order of prevalence) (In Northern Europe)
Pollen is well-preserved in many soils, and is readily
recognisable under the microscope; therefore, if, for
instance, the pollen content of soil from a peat-bog be