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TWENTY-FOUR-HOUR DIAL ILLUSTRATING HUMAN CHRONOLOGY[2]

Twenty-five thousand years equals one hour

[Illustration: Twenty-four hour dial]

Age of modern man 10,000 years = less than half an hour.
Age of Cro-Magnon type 25,000 years = one hour.
Age of Neanderthal type 50,000 years = two hours.
Age of Piltdown type 150,000 years = six hours.
Age of Heidelberg type 375,000 years = fifteen hours.
Age of Pithecanthropus 500,000 years = twenty hours.

Beginning of Christian era 2,000 years = 4.8 minutes.
Discovery of America 431 years = about 1 minute.
Declaration of Independence 137 years = about 21 seconds.

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There are four main methods of determining prehistoric {60} time.[3]
One is called the (1) _geologic method_, which is based upon the fact
that, in a slowly cooling earth and the action of water and frost, cold
and heat, storm and glacier and volcanic eruption, the rocks on the
earth are of different ages. If they had never been disturbed from
where they were first laid down, it would be very easy to reckon time
by geological processes. If you had a stone column twenty feet high
built by a machine in ten hours' time, and granting that it worked
uniformly, it would be easy to see just at what hour of the period a
layer of stone four feet from the bottom, or ten feet from the top, was
laid. If, however, in the building of the wall, it should have toppled
over several times and had to be rebuilt, it would require considerable
study to see just at what hour a certain stone was put in the wall.
Studying the geology of the earth in a large way, it is easy to
determine what strata of the earth are oldest, and this may be verified
by a consideration of the process in which these rocks were being made.
Chemistry and physics are thus brought to the aid of geology. It is
easy to determine whether a rock has been fused by a fire or whether it
has been constructed by the slow action of water and pressure of other
rocks. If to-day we should find in an old river bed which had been
left high and dry on a little mesa or plateau above the present river
bottom, layers of earth that had been put down by water, and we could
find how much of each layer was made in a single year, it would be easy
to estimate the number of years it took to make the whole deposit.
A