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300406-22. © NRT, 2006
Limestone pavement near Gaping Gill, Ingleborough, Yorkshire Dales National Park, UK, 30 April, 2006

It's not always appreciated that the area's world-renowned exposures of limestone pavement were actually formed primarily by gradual dissolution of hard*, horizontally-bedded limestone below the ground surface.
Debris left by retreating glaciers formed a protective layer over the bedrock. Colonised by forest, it was mildly acidic water percolating through the soil which preferentially cut into joints in the rock (grikes), leaving the faces of the intervening limestone blocks (clints) relatively intact; had they been exposed to wind and rain, the blocks would have eroded faster too.
Subsequent deforestation, grazing and, now, visiting walkers have eroded away the surface soil, gradually exposing the pavement, as seen in the background. This reverse-angle view of the same location shows a 'cross-section' through the result.

*: It does have to be hard limestone: pavement can't form on chalk, for example. In Britain that means Carboniferous limestone in northern England and Ireland, though some examples in Scotland have formed on drastically older rock.

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Day in the life... © NRT, 2006