FERNS, FOSSILS AND FUEL 
of cycads also had developed something like big flowers, 
although they cannot be considered as true flowering 
plants. What the color of the cycads and of the two 
flowering plants (angiosperms) was, it is impossible to 
say positively. Since the insects of the period were at¬ 
tracted by the flowers and helped their pollination, we 
must take it for granted that bright colors like red, blue, 
and white, were represented in the Jurassic forests. 
Nevertheless, the angiosperms were just bginning. They 
do not come into their own until much later, in the Upper 
Cretaceous period. 
The early Jurassic climate may have had seasonal 
variations, for we find annual rings in the fossil woods 
from that time. The climate of the main part was warm 
and uniform, and the fossil woods have no annual 
markings. 
The next period, the Cretaceous, is divided into two 
distinct sections. The Lower, or earlier Cretaceous, is 
much like the Jurassic, so far as flora and fauna are con¬ 
cerned. Some of the finest fossil cycad trunks were found 
in the Lower Cretaceous rocks of the Black Hills in west¬ 
ern South Dakota. At the end of the Lower Cretaceous, 
a great change suddenly took place. The angiosperms, 
or true flowering plants, suddenly overran the vegetation 
of the earth. Just as the migration of the Teutonic na- 
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