EIGHT 
THE ROMANCE OF COAL AND OIL 
F OSSIL plant remains have another interest for us 
in addition to the picture they give us of the world 
as it appeared in former ages. Their close relation to 
coal and to oil, two very important commodities of mod¬ 
ern civilization, makes a knowledge of them highly desir¬ 
able for practical purposes. They are also very valuable 
as indicators of geologic levels or horizons. 
When the geologic formations in some locality are 
studied with the help of type sections, a certain for¬ 
mation or series of formations is usually found to be 
exceptionally well exposed. It is possible to examine in 
such places a consecutive series of sediments which rep¬ 
resent a considerable portion of geologic chronology. By 
the combination and comparison of numerous type sec¬ 
tions, the entire history of Paleozoic, Mesozoic, and 
Cenozoic rocks was established. 
The various horizons of these sections contain plant 
and animal fossils which are characteristic of the sections. 
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