Shetland is full of spectacular and often ancient metamorphic rocks like this cliff, which is formed of gneiss banded with granitic intrusions. The age of these rocks is uncertain, but they are probably over 500 million years old. The rocks started out as sediments, probably sandy deposits, which were buried deep in the crust of the Earth by later deposition. This subjected them to extremes of temperature and pressure which brought them close to the point of melting. They were also intruded by bands of granitic rock, and the whole lot was deformed by what would appear to be complex folding, producing the 'marble cake' effect. Finally, they were uplifted and exhumed, probably by a combination of tectonic movement and surface erosion, with the structure further exposed by the relatively recent marine erosion which has formed the cliff itself.

Based on explanation from Anne Burgess, although any errors in the explanation are certainly mine.