These are trees that have come to the Gorge since white settlement. They include blackwood trees and trees that are often found in the Mallee. A possible reason for this is seeds deposited from bird droppings.
The Werribee River in the base of the Werribee Gorge near Myrniong. The rocks in the river contain white stones mixed with lava, and the white rocks show scratch marks that can be identified under an electron microscope. They indicate these scratch marks were made with pressure from a glacier. These rocks can be found in several other places in the Werribee River over its entire lengh.