Oil shales are essentially dull coals that formed from small plant fragments that settled out on the ancient lake bottom.
(Oil shales; are; essentially dull coals that formed from small plant fragments) (essentially dull coals; formed; from small plant fragments) (small plant fragments; settled out; )
Oil shales essentially dull coals small plant fragments
are formed settled out
essentially dull coals that formed from small plant fragments
from small plant fragments