FERNS, FOSSILS AND FUEL 
venation of the leaves. The grasses, wild flowers, and 
small shrubs did not shed leaves, but withered and 
decayed on the spot. They were therefore unable to 
supply us with fossils. There are only a few seeds and 
flowers known from that time, and occasionally the leaves 
of water lilies which had been buried in the mud. 
With the Upper Cretaceous period, we are able, for 
the first time, to connect the plant life directly with that 
of our own day, because it is so closely related to the 
floras growing at present. The Cretaceous flora as well 
as the later floras of the Tertiary period can best be 
studied by starting from our present vegetation and fol¬ 
lowing the successive horizons downward. When we 
were dealing with the Paleozoic and Mesozoic plant 
life, we had to follow the opposite method and take as 
a starting point the Devonian period in the Paleozoic 
era and the Triassic period in the Mesozoic, and study 
the successive floras in an upward direction from earlier 
to later. But the paleobotanists who specialize in Upper 
Cretaceous and Tertiary plants work from the living 
types down to the earlier because of the close relation 
between them. 
The animal life of the Upper Cretaceous period, how¬ 
ever, was still distinctly Mesozoic. The animal change 
did not come until the following period. Gigantic rep- 
86 
