This peat accumulates slowly and gradually today (estimated at between 1 and 4 millimetres per year), so geologists who believe that 'the present is the key to the past' conclude that the plant debris found in coal seams must have formed slowly and gradually from plant debris accumulating as peat in the bottom of swamps.
(This peat; accumulates slowly; T:today) (the plant debris; found; L:in coal seams) (plant debris; accumulating; )
This peat the plant debris plant debris
accumulates slowly found accumulating
T:today
L:in coal seams