It is possible to make a detour from the standard Phototrail route in order to examine part of the North Craven Fault. After visiting the Norber Erratics return to the wooden signpost. Instead of heading for Austwick follow the path marked 'Crummack'. The path is quite distinct and weaves its way through boulders and small trees, passing quite close to a remarkable boulder split in two by a large hawthorn bush. Continue in the same direction for about 100 metres to reach a stile in the wall. Climb the stile and go down the small pasture to another stile 100 metres away. Before you cross this second stile be aware of the drop below the path, and the potential of loose rock above. Follow the path on a wide ledge below a tree-covered cliff. This is Nappa Scar and it is here that the North Craven Fault can be seen.
A Sketch of the rocks at Nappa Scar
Above the path in the base of the cliff you can see the older Silurian rocks overlain by a mixture of pebbles cemented together by limestone. This matrix is called a conglomerate. The pebbles, made up of Silurian greywacke and slate, get progressively smaller the farther up you look. The conglomerate is in turn overlain by Carboniferous limestone. It is possible to see a repeat of this sequence of greywacke / slate, conglomerate, and limestone below the path, having been down-faulted. The throw of this is only 10 or 20 metres, providing evidence that in this locality the North Craven Fault is a series of small step faults rather than one big fault.
It may be possible to see water flowing out from the base of the limestone where an underground stream resurges into daylight. These springs are often used as local water supplies. A water tank screened by a stone wall can be seen on the hillside with a small water treatment building at the bottom of the field. There is no right of way down into the field and unless you are heading into Crummackdale the easiest route is to retrace your steps back to the signpost.
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