Question

In this excerpt from "Colonialism in the United States" by Henry

Answer 1

Long after the world to which it belonged has vanished, a habit of thought will live on, indelibly imprinted upon a race or nation, like the footprint of some extinct beast or bird upon a piece of stone. 

The word indelibly refers to the anything that is impossible to remove or forget. It is the mark that cannot be erased.