“When we got close to the rocks in the quarry, we could see their banding was typical of Lewisian gneiss,” says Paul. Lewisian gneiss is metamorphic rock, which means it was formed by being heated up ...

It is unresolved whether the gneisses are basement rock to the metasedimentary complex or whether the two complexes represent one protolithic package with the gneiss a higher metamorphic grade ...