Throughs La on eroded Woodbine Shale

Sandside and Storth are in the Arnside and Silverdale Area of Outstanding Natural Beauty on the eastern edge of the Kent estuary. The area is of Limestone rock of which there are three main units, the oldest is Dalton Limestone then Park and finally Urswick Limestone. Though the units were laid down horizontally they have since been turned to the vertical and even tipped over a little further.

The trail starts at The Ship Inn where we parked for the price of a welcome drink at the end of the trip. From the car park is a view across the Kent estuary towards the Lakes, Whitbarrow Scar, also of the same 3 limestone beds, Borrowdale Volcanic rocks of the Langdales and the Silurian rocks of the outer hills.

Just behind the pub is Sandside Cutting, the site of the old railway track, walking along here there are large cliffs of the limestone on either side. We found evidence of Dalton Limestone rock beds, here vertical, moving against each other leaving scratches, Slickensides, and fossils of Coral. We were especially grateful that someone keeps these areas relatively clear of vegetation giving good access and views.

Slickensides in cutting

Fossil corals in cutting

Jutting towards us was a large vertical area of curving rock surrounded on either side by what looked like big layers of onion. This was a fold in the rock beds where the other beds had been partly removed by the formation of the cutting.What forces must have been involved in folding and tipping these rock beds.

Folding in cutting

Outside two houses we saw large pieces of Urswick Limestone pavement standing on end forming gate posts. Really good to see the Urswick but a practice long since prohibited. Walking up to the village of Storth we passed  rock outcrops in two opposite gardens, these having been separated by a fault and moved 30metres apart.

A flattish field and a playing field had been created by the passage of a glacier from the central Lakes about 20,000 years ago. We were now walking on the Park Limestone but buried under the glacial cover.

Throughs Lane has been formed by the shale layer having been more eroded than the harder Urswick Limestone on either side. The Urswick beds formed in a similar way to our Yoredale rock beds, where a river runs into a shallow sea, sand and gravel and later silt layers upwards before the sea level rises a little and limestone forms on top in the warm shallow sea. This cycle is repeated several time producing this layering.

As we walked back down towards the estuary, again with wonderful views of the Lakeland fells and a Drumlin field, we looked in the field walls and found rocks of Borrowdale Volcanic and Silurian origin, in a wood a large volcanic rock boulder and another of Shap Granite. These were all known as erratics, rocks plucked from their source and transported by the glaciers. 

It was an excellent walk with great geological interest and a real challenge to get ones head round the 4D of Geology the 4th being the time lapses. We were very grateful to Peter Standing the author of the Geotrail and Janet Brady for her illustrations and for making it available as an on line pdf available to all at :-

Erratic (1)-on limestone


Rock types in wall

Josephine Drake

Text by Dr J Drake, Images by Ian Hughes