nderstand why the first creatures on earth left no
trace. The first real fossils found in the rocks are the hard shells or
skeletons of the first plants and animals that had hard parts.

AN ANCIENT BEACH AT EBB TIDE

When the tide is out, the rocks on the Maine coast have plenty of living
creatures to prove this northern shore inhabited. Starfishes lurk in the
hollows, and the tent-shaped shells of the little periwinkle encrust the
wet rocks. Mussels cling to the rocks in clumps, fastened to each other
by their ropes of coarse black hair. The furry coating of sea mosses
that encrust the rocks is a hiding-place for many kinds of living
things, some soft-bodied, some protected by shells. The shallow water is
the home of plants and animals of many different kinds. As proof of this
one finds dead shells and fragments of seaweeds strewn on the shore
after a storm.

Along the outer shores of the Cape Cod peninsula and down the Jersey
coast, the sober colouring of the shells of the north gives way to a
brighter colour scheme. In the warmer waters, life becomes gayer, if we
may judge by the rich tints that ornament the shells. The kinds of
living creatures change. They are larger and more abundant. The seaweeds
are more varied and more luxuriant in growth.

When we reach the shores of the West Indian islands and the keys of
Florida the greatest abundance and variety of living forms are found.
The submerged rocks blossom with flower-like sea anemones of every
colour. Corals, branching like trees and bushes on the sea floor, form
groves under water. Among them brilliant-hued fishes swim, and highly
ornamented shells glide, as people know who have gazed through the glass
bottoms of the boats built especially to show visitors the wonderful sea
gardens at Nassau, Bahama Islands, and at Santa Catalina Island,
southern California.

On every beach the skeletons of animals which die help to build up the
land; though the process is not so rapid in the north as on the shores
that approach the tropics. The coast of Florida has a rim of island
reefs around it built out of coral limestone. Indeed, the peninsula was
built by coral polyps. Houses in St. Augustine are built of coquina
rock, which is simply a mass of broken shells held together by a lime
cement. Every sea beach is packed with shells and other remnants of
animals and plants that live in the shallow waters. Deeper and deeper
year by year the sand buries these skeleton