The study of the deltas of the Nile, the Ganges, and the
Mississippi has taught us how slow is the wearing action of water, how
vast its effects when time is allowed for its operation. The reefs of
the Pacific, the deep-sea soundings of the Atlantic, show that it is to
the slow-growing coral and to the imperceptible animalcule, which lives
its brief space and then adds its tiny shell to the muddy cairn left by
its brethren and ancestors, that we must look as the agents in the
formation of limestone and chalk, and not to hypothetical oceans
saturated with calcareous salts and suddenly depositing them.
And while the inquirer has thus learnt that existing forces--'give them
time'--are competent to produce all the physical phenomena we meet with
in the rocks, so, on the other side, the study of the marks left in the
ancient strata by past physical actions shows that these were similar
to those which now obtain. Ancient beaches are met with whose pebbles
are like those found on modern shores; the hardened sea-sands of the
oldest epochs show ripple-marks, such as may now be found on every
sandy coast; nay, more, the pits left by ancient rain-drops prove that
even in the very earliest ages, the "bow in the clouds" must have
adorned the palaeozoic firmament. So that if we could reverse the
legend of the Seven Sleepers,--if we could sleep back through the past,
and awake a million ages before our own epoch, in the midst of the
earliest geologic times,--there is no reason to believe that sea, or
sky, or the aspect of the land would warn us of the marvellous
retrospection.
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