Read More About It - Tropical Upland Forest:
Bouncing Landscape

During the early Pennsylvanian, the plates carrying North America and Europe were colliding with Gondwana, the supercontinent to the south. The force of the collision caused Illinois to be shifted up and down. As the shallow seas that had covered Illinois for almost 230 million years drained away, They were replaced by lowland swamps. The swamps were periodically flooded as sea levels continued to rise and fall.