unconformity

The sites include familiar ones, such as the Grand Canyon’s “great unconformity,” a billion-year gap in the rock record erased by erosion.

An “unconformity” is the geological term for “a discontinuity in the deposition of sediment,” in Raffles’s words.

It echoes James Playfair’s description of the “abyss of time” he glimpsed while viewing a strata unconformity at Siccar Point in 1788, when geology was first emerging as a science.

An unconformity: At Mount Stimson, the rover identified from sol 980 a thick sandstone unit overlying the lake deposits, separated by a geological feature called an unconformity.

This unconformity represents a time where erosive processes took over after millions of years when the lake had finally dried up - to form a new land surface.