duration, have we any means of determining even approximately the length
of the period to which we ourselves belong? If so, it may furnish us
with some data for the further solution of these wonderful mysteries of
time, and it is besides of especial importance with reference to the
question of permanence of Species. Those who maintain the mutability of
Species, and account for all the variety of life on earth by the gradual
changes wrought by time and circumstances, do not accept historical
evidence as affecting the question at all. The monuments of those oldest
nations, all whose history is preserved in monumental records, do not
indicate the slightest variation of organic types from that day to this.
The animals that were preserved within their tombs or carved upon their
walls by the ancient Egyptians were the same as those that have their
home in the valley of the Nile today; the negro, whose peculiar features
are unmistakable even in their rude artistic attempts to represent them,
was the same woolly-haired, thick-lipped, flat-nosed, dark-skinned being
in the days of the Rameses that he is now. The Apis, the Ibis, the
Crocodiles, the sacred Beetles, have brought down to us unchanged all
the characters that superstition hallowed in those early days. The
stony face of the Sphinx is not more true to its past, nor the massive
architecture of the Pyramids more unchanged, than they are. But the
advocates of the mutability of Species say truly enough that the most
ancient traditions are but as yesterday in the world's history, and that
what six thousand years could not do sixty thousand years might effect.
Leaving aside, then, all historical chronology, how far back can we
trace our own geological period, and the Species belonging to it? By
what means can we determine its duration? Within what limits, by what
standard, may it be measured? Shall hundreds, or thousands, or hundreds
of thousands, or millions of years be the unit from which we start?

I will begin this inquiry with a series of facts which I myself have