gain pick up the thread we are surrounded by more advanced types,
higher forms of life. Though we may hope that future discoveries will do
much toward completing the records, we can not hope that they will ever
really be perfected. So, from our present stand-point, the history of
life on the globe falls naturally into three great divisions.<6> This
is no more than we might expect, when we reflect that nature's laws
are universal in their action, and that the world, as a whole, has been
subjected to the same set of changes.

The period following on after Archean time is called, by geologists,
Paleozoic time.

During the long course of time embraced in this age, the forms of life
present wide differences from those of existing time.

This period produced the great beds of coal we use to-day. But the
vegetation of the coal period would present strange features to our
eyes. The vegetation commenced with the lowest orders of flowerless
plants, such as sea-weeds; but, before it was brought to a close, there
was a wonderful variety and richness of plants of the flowerless or
Cryptogamic division. In some of the warmest portions of the globe,
we have to-day tree-ferns growing four or five feet high. During the
closing part of the Paleozoic time, there were growing all over the
temperate zone great tree-ferns thirty feet or so in height. Some
varieties of rushes in our marshes, a foot or two in height, had
representatives in the marshes of the coal period standing thirty feet
high, and having woody trunks.<7> Near the close of the Paleozoic
time, vegetation assumed a higher form of life. Flowering plants are
represented. Pines were growing in the coal measures.

In animal life a similar advance is noted. The class of animals having
no backbone, or invertebrate animals, were largely represented. But,
toward the close of the Paleozoic time, we meet with representatives of
the backbone family. The waters swarmed with fishes.<8> Besides these,
there were amphibians; <9> and reptiles in the closing portions.<10>

Illustration of The Pterodactyl.--------------

Thus we see what a great advance was made in life during this period.
The forms of life during the early stages of this age were inferior in
this, also, that they were all water species.<11> But, before it closes,
we have a rich and varied terrestrial vegetation, and also air-breathing
animals. The class Mammalia, to which man belongs, had no representative
on the earth