This process continued for a long period of time until the vegetation was decayed and buried, forming a coal seam.
(This process; continued; T:for a long period of time; T:until the vegetation was decayed and buried) (the vegetation; buried; ) (This process; forming; a coal seam)
This process the vegetation This process
continued buried forming
T:for a long period of time T:until the vegetation was decayed and buried
a coal seam