FERNS, FOSSILS AND FUEL 
insect forms. Many cockroaches, however, climbed over 
the plants. There have been found over a thousand 
fossil cockroach species, more than half of which lived 
in the Pennsylvanian period. The waters were full of 
fish and little crustaceans, but the big trilobites had by 
this time disappeared. The oceans had a vigorous animal 
and plant life, but while the land floras had attained a 
high development, the land animals were still in an 
early stage and far behind their marine contemporaries. 
The swamps were filled not only with living plants 
but with an enormous quantity of dead plant matter. 
Dead stems, leaves, spores, and seeds were often piled 
many feet high. 
The low mountains may also have been covered with 
forests of lycopods and tree-ferns, though few traces of 
this vegetation have survived. The sky was probably 
cloudy most of the time, and the air full of moisture 
and warm all the year round. There was no change 
of seasons, no fall and winter, only an eternal spring 
and summer. If a person could be transplanted into 
one of these Pennsylvanian swamp forests, he would not 
feel a greater change than if he went from the temperate 
zone to a jungle along the Amazon river. In spite of 
the absence of flowers, the general type of plant life 
was not greatly different from our own. The species 
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