244

The Sky in Autumn 244

PART I

THE EARTH

* * * * *

THE GREAT STONE BOOK

"The crust of our earth is a great cemetery where the rocks
are tombstones on which the buried dead have written their
own epitaphs. They tell us who they were, and when and where
they lived."--_Louis Agassiz._

Deep in the ground, and high and dry on the sides of mountains, belts of
limestone and sandstone and slate lie on the ancient granite ribs of the
earth. They are the deposits of sand and mud that formed the shores of
ancient seas. The limestone is formed of the decayed shells of animal
forms that flourished in shallow bays along those shores. And all we
know about the life of these early days is read in the epitaphs written
on these stone tables.

Under the stratified rocks, the granite foundations tell nothing of life
on the earth. But the sea rolled over them, and in it lived a great
variety of shellfish. Evidently the earliest fossil-bearing rocks were
worn away, for the rocks that now lie on the granite show not the
beginnings, but the high tide of life. The "lost interval" of which
geologists speak was a time when living forms were few in the sea.

In the muddy bottoms of shallow, quiet bays lie the shells and skeletons
of the creatures that live their lives in those waters and die when they
grow old and feeble. We have seen the fiddler crabs by thousands on
such shores, young and old, lusty and feeble. We have seen the rocks
along another coast almost covered by the coiled shells of little gray
periwinkles, and big clumps of black mussels hanging on the piers and
wharfs. All these creatures die, at length, and their shells accumulate
on the shallow sea bottom. Who has not spent hours gathering dead shells
which the tide has thrown up on the beach? Who has not cut his foot on
the broken shells that lie in the sandy bottom we walk on whenever we go
into the surf to swim or bathe?

Read downward from the surface toward the earth's centre--

TABLE OF CONTENTS

------+----------------------+-----------+-----------------------
Part | _Rock Systems_ | _Dominant | _Dominant Plants_
| | Animals_ |
------+----------------------+-----------+-----------------------
VII. | Recent | Man | Flowering kinds