The most enduring rocks are the oldest; and the most perishable are,
as a rule, the youngest. It takes time to season and harden the
rocks, as it does men. Then the earlier rocks seem to have had
better stuff in them. They are nearer the paternal granite; and the
primordial seas that mothered them were, no doubt, richer in the
various mineral solutions that knitted and compacted the sedimentary
deposits. The Cretaceous formations melt away almost like snow. I
fancy that the ocean now, compared with the earlier condition when
it must have been so saturated with mineral elements, is like
thrice-skimmed milk.

The geologist is not stinted for time. He deals with big figures. It
is refreshing to see him dealing out his years so liberally. Do you
want a million or two to account for this or that? You shall have it
for the asking. He has an enormous balance in the bank of Time, and
he draws upon it to suit his purpose. In human history a thousand
years is a long time. Ten thousand years wipe out human history
completely. Ten thousand more, and we are probably among the rude
cave-men or river-drift men. One hundred thousand, and we
are--where? Probably among the simian ancestors of man. A million
years, and we are probably in Eocene or Miocene times, among the
huge and often grotesque mammals, and our ancestor, a little
creature, probably of the marsupial kind, is skulking about and
hiding from the great carnivorous beasts that would devour him.

"Little man, least of all,
Among the legs of his guardians tall,
Walked about with puzzled look.
Him by the hand dear Nature took,