Flutings are channels scored in steep slopes. They are found on granite bornhardts, blocks and boulders, and occur in a wide range of climatic conditions. Rivulets and seepages charged with chemicals and biota are capable of attacking and degrading granite, and this can occur below the surface, at the weathering front and on outcrops. Many, perhaps most, flutings are of subsurface provenance, but on exposed surfaces, algal coatings develop and so protect the beds. Abandonment and inversion of such flutings—the conversion of channels protected by algae into ribs — are the result of the comparative weakness of the adjacent unprotected laminated rock exposed in the erstwhile, commonly flared, weathering front. At some sites, newer, lateral, channels are eroded through the laminated rock to expose fresh rock in 'button-holes'. Elsewhere, however, deep localised erosion has taken place on ribs on which the algal veneer has deteriorated.
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