Of all the terms used to describe features of the land, this one— bedrock—is most often called up in literature and religion as a metaphor for steadfast dependability, comfort, and security. It’s a true enough allusion: the rock that lies hidden deep beneath layers of topsoil and subsoil can be relied upon not to change its composition. It does not weather or shift in response to the capricious atmospheric forces that constantly rearrange the more superficial elements of the landscape. Although any sense of the Earth as unchanging is ultimately an illusion (the very continents are moving, in fact, at a rate of an inch or more per year), from the perspective of a human lifetime the bedrock may be counted on not to change perceptibly. It seems to lie immutable beneath our feet and serves as a foundation and parent material to the land, both structurally and chemically, since its mineral composition, permeability, and other characteristics may greatly influence the layer that forms above it.

Barbara Kingsolver