far being
almost confined to the water. A few insects make their appearance and
a few thousand-leggers are running around among the lowly plants; a
few spider-like animals have arisen; there are a few snails that have
left the water and taken to the land. Altogether only the dawn of a
land fauna is to be noticed. In the Devonian the plants are creeping
up upon the ground. Ferns are growing about everywhere, though they
are not exactly our ferns, but are rather a sort of intermediate form
between these and the present seed plants.

Now comes an entire change in the history of the world. By some means
a rise in the bottom seems to have cut off a great part of the
internal sea from the outer ocean and to have converted it into a
widespread shallow bay, much like the sounds which lie back of the
islands that line the Atlantic Coast from New Jersey to Florida. Just
as this coastal region to-day is covered with salt marshes, so the
whole internal sea of the Carboniferous period was converted into a
great swamp. Sometimes an oscillation of the crust of the earth
brought this marsh above the surface of the sea and a luxuriant growth
of plants spread over it. Then a sinking of the bottom allowed the mud
and sand to wash down the shores, and spread out over the marsh, and
enclose the muck of the marsh under a layer of sand or clay. Another
lift of the bottom would start the swamp growing once more, and a
series of alternations between marsh land and sound seems to have
followed. The plants of this period are not the plants of to-day,
though we still have some very degenerate representatives of them. The
common horse-tail, with its angular, slender, leaflike branches and
its club-shaped spore-bearing body, is a modern degenerate descendant
of the treelike calamites of the Carboniferous forest. A creeping
evergreen, known by the name of clubmoss, is in like manner the modern
degenerate remnant of the scalestem and sealstem, which were the great
trees of the forests of the coal period.

All over the surface of the marsh, between these big trees, grew the
ferns. While the coal itself was formed generally from the scalestems
and sealstems, the most common fossils found in the shales that lie
upon the coal beds are the ferns which covered the surface of the
marsh.

It is believed by many geologists that this great luxuriant forest
points to a time when the climate was far warmer than it is to-day,
when the air was moist and heavil