The geologically famous boulders on the hillside at Norber are some of the best examples of glacial erratics in the country. The boulders at Norber, or the North Hill, have the peculiar feature that they are older than the rock on which they now rest. They lie scattered together, mostly within a space of a half-mile, and are of every shape and size.

The major rock types in the area are carboniferous limestone, formed some 330 million years ago on the floor of a shallow sea, and heavily folded Silurian greywacke and slate which were formed some 100 million years earlier. During the last Ice Age 13,000 years ago, the glacier flowed south out of Crummackdale and over the brow of the hill eroding and plucking up the silurain greywacke and slate and transporting it southwards about one kilometre, the trip taking several thousands of years.

When the ice melted, the transported material was deposited on top of the carboniferous limestone and have acted as natural umbrellas, sheltering the limestone from weathering and erosion. Whilst the general surface of the limestone bedrock has been lowered by about 0.5 metres, the erratics have been left standing on small plinths of protected limestone or lie piled one on another in the most fantastic manner.