carbonized plant material is commonly found between easily separated sedi-
ment layers (Fig. 111). Animals were also buried in the great ancient coal
swamps, where their bones were preserved and fossilized.FOSSIL FUELS
The Carboniferous and Permian had the highest organic burial rates of any
period in Earth history. Extensive forests and swamps grew successively on top of
each other and continued to add to thick deposits of peat, which were buried
under layers of sediment. The weight of the overlying strata and heat from the
planet’s interior reduced the peat to about 5 percent of its original volume and
metamorphosed it into lignite as well as bituminous and anthracite coal.
The world’s coal reserves far exceed all other fossil fuels combined.They
are sufficient to support large increases in consumption well into this century.Figure 110Fossil leaves
of the tree fern
Neuropteris,Fayette
County, Pennsylvania.
(Photo by E. B. Hardin,
courtesy USGS)
Historical Geology