There, in the Calhoun Coal of the Mattoon Formation, which is a 302-million-year-old swamp deposit, a large variety of exquisitely preserved plant fossils make up a paleoentomologist&#146;s ideal amusement park.
(the Calhoun Coal of the Mattoon Formation; is; a 302-million-year-old swamp deposit)
the Calhoun Coal of the Mattoon Formation
is
a 302-million-year-old swamp deposit