The six-stage fossilisation process is illustrated below. It involved two flooding events (one killing the trees and a later one filling the hollow stumps). The timing was crucial – the stumps needed to have decayed to become hollow but not completely rotted away. A rare coincidence!
1. The living trees were killed when the area in which they were growing was flooded and the water deposited sand and mud around them.
2. The trunks projecting above the sediment broke off and were washed away.
3. The stumps decayed in the middle leaving only the outer bark.
4. More sediment was then washed into the now hollow stump and roots.
5. While deeply buried, the sand and mud were converted into solid rock and the bark to a very thin layer of coal.
6. After discovery, the rock outside the stumps and the coal layer were removed to leave the sandstone casts of the inside of the trees visible today.