scheme of
the evolution of life is written on the face of living nature; and it
is written again, in blurred and broken characters, in the embryonic
development of each individual. With these aids we set out to restore
the lost beginning of the epic of organic evolution.

CHAPTER VI. THE INFANCY OF THE EARTH

The long Archaean period, into which half the story of the earth is so
unsatisfactorily packed, came to a close with a considerable uplift of
the land. We have seen that the earth at times reaches critical stages
owing to the transfer of millions of tons of matter from the land to the
depths of the ocean, and the need to readjust the pressure on the crust.
Apparently this stage is reached at the end of the Archaean, and a great
rise of the land--probably protracted during hundreds of thousands of
years--takes place. The shore-bottoms round the primitive continent are
raised above the water, their rocks crumpling like plates of lead
under the overpowering pressure. The sea retires with its inhabitants,
mingling their various provinces, transforming their settled homes. A
larger continent spans the northern ocean of the earth.

In the shore-waters of this early continent are myriads of living
things, representing all the great families of the animal world below
the level of the fish and the insect. The mud and sand in which their
frames are entombed, as they die, will one day be the "Cambrian" rocks
of the geologist, and reveal to him their forms and suggest their
habits. No great volcanic age will reduce them to streaks of shapeless
carbon. The earth now buries its dead, and from their petrified remains
we conjure up a picture of the swarming life of the Cambrian ocean.

A strange, sluggish population burrows in the mud, crawls over the sand,
adheres to the rocks, and swims among the thickets of sea-weed. The
strangest and most formidable, though still too puny a thing to survive
in a more strenuous age, is the familiar Trilobite of the geological
museum; a flattish animal with broad, round head, like a shovel, its
back covered with a three-lobed shell, and a number of fine legs or
swimmers below. It burrows in the loose bottom, or lies in it with
its large compound eyes peeping out in search of prey. It is the chief
representative of the hard-cased group (Crustacea) which will later
replace it with the lobster, the shrimp, the crab, and the water-flea.
Its remains form from a third to a fourth of all the bur