When you cross Manor Bridge leaving Swilla Glen and the Great Scar Limestone anticline behind, you will eventually notice a change in lithology. On the right bank of the Twiss Upper Ordovician calcareous siltstones of the Norber Formation are exposed along the path. A little further on, the left bank becomes dominated by a steeply inclined limestone face. This is the fault plane of the North Craven Fault (footwall).
The Ordovician calcareous siltstone (footwall) contrast nicely with the limestone. You can see that the calcareous siltstones are contorted (deformed) and have yielded a sparse fossil fauna. Also you will notice a 'cave' or more likely a failed attempt to find lead mineralisation. If you are eager for a closer inspection by crossing the Twiss you should look out for:
a) Vertical grooving and oblique slickensiding on the fault plane.
b) A lamprohyre dyke cutting the Ordovician siltstones. The volcanic rock is a medium grained crystalline rock rich in biotite and quartz.
More dramatic slickensides and a mineral breccia can be seen further along the Twiss but you will have to climb up a height to see it!