Crummack Dale lies behind and above the village of Austwick and is an area where we can see the rocks, known as the Craven Inliers, Silurian rocks, that lie below the Carboniferous limestone that we are used to seeing in the Yorkshire Dales.

We climbed the hill out of Austwick noting many large rocks lying strewn about the upper fields, often covered in a beautiful yellow green lichen in map like shapes, Rhizocarpon geographicum, which is known to grow on sandstone and not on limestone.

Silurian sandstone rock with Rhizocarpon Lichen

Finally we reached the Norber Erratic Field, where more of the lichen covered rocks were often standing on pedestals of limestone suggesting transport of some power having moved these older rocks from elsewhere on to the top of younger limestone. Different rates of weathering have helped form the pedestals.

A Norber Erratic pedestal, Silurian sandstone on a limestone pedestal

We climbed down through limestone outcrops to the Sub-Carboniferous Unconformity at Nappa Scars, a cliff face with an undercut area of very different appearance, pebbly in a limestone matrix  lying on a siltstone base. The sequence of events forming this cliff face is deep sea deposition of sands and mud in Silurian times, followed by a time gap, the Unconformity, representing the removal by erosion  of all the Devonian rocks formed on land, then a rising sea level washed in pebbles from surrounding areas across a beach. As the sea deepened in a warm tropical climate the Carboniferous limestone was formed above.

The basal Silurian Sandstone covered by pebbly limestone with the base of the Great Scar Limestone above

We walked north on Crummack Lane noting the field from which the erratics had been plucked by a grinding Glacier then transported south but uphill over a brow and onto the Norber Erratic Field.

The source of the Norber Erratics

Walking northeast on a field footpath we walked over hills of rock formed by Anticlines and a Syncline, folds of rock into hills and dips respectively, which could also be seen against each hillside.

We reached our lunch spot and looked in the stream to find some fascinating looking red and green striped rocks at Moughton Whetstone Hole. The rings are Liesegang Rings, formed by oxidation of the iron in the rocks during the Devonian and early Carboniferous when the rocks were part of a continent. They were later worked to produce Whetstone or sharpening stones.

Moughton Whetstone with Liesegang Rings

As we returned down the Green lane we were able to look up to the left hand cliff face and once again see upper horizontal limestone lying on almost vertical rocks above the screes, another Unconformity. The screes of loose rock were formed by periglacial weathering, the effects of freezing and thawing of the rocks.

The Studrigg Unconformity

The flowers throughout the day were an added pleasure, particularly the early Townhall Clock and the later Bird’s Eye Primrose.

By the time the five of us returned to Austwick the earlier rain and dullness had disappeared and been replaced by lovely sunshine, and reflected our mood of satisfaction at a good days mental and physical exercise.

Leader Josephine Drake

Photos Ann Shaw