Harrow and Hillingdon Geological Society

Yorkshire Dales

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Previous Trips

An unofficial start to the weekend was made at the disused Hulme Quarry, now part of the Park Hill Country Park near Stoke-on-Trent. This is an SSSI with great exposures of the lower Triassic Bunter pebble beds of the Sherwood Sandstone Group. The pebble beds are texturally mature pebble/cobble conglomerates arranged in poorly sorted horizontal sheets on better sorted cross-bedded sets. Thick sheets of conglomerate are associated with interbedded sandstones. This is an important site for studying environmental conditions that existed in the Triassic. There are good paths both around and through the quarry.

Friday morning dawned bright and warm and we walked from Austwick up to the Norber Erratics and then over to Nappa Scar. The Erratics are glacially transported sandstone boulders eroded from the cliffs 1km away to the north and deposited on Carboniferous limestone. Some of the larger erratics have protected the limestone beneath them from erosion while the surrounding surface has dissolved away.

The Nappa Scar path is reached by a wide ledge below a tree covered cliff and it is here that the North Craven Fault can be seen. The older Silurian rocks are overlain by conglomerate which is in turn overlain by Carboniferous limestone. At this locality the North Craven Fault is a series of small step faults rather than one big fault. Spring water flows out from the base of the limestone.
Fields around here were full of sheep and their young lambs – at least they didn’t have the problems of negotiating the stone ladder stiles in the walls!

In the afternoon we drove along a narrow road up to Combs Quarry in Foredale. This exposes one of the best angular unconformities in the Lower Palaeozoic craven inlier. Basement rocks are Silurian (Horton Formation) and have been tilted before being eroded while the overlying limestone is Lower Carboniferous. Thin inter-beds of bentonite (off-white volcanic clay) were in the basal member of the Horton Formation. A row of old quarry cottages attracted several photographs.

We then visited the Ribblehead Viaduct, the 24-arched viaduct on the Settle-Carlisle railway but found it difficult to work out where the old construction site had actually been.

Saturday, another glorious day, and with a full complement of participants, we were off to the Sedgwick Geological Trail. The trail takes you along the banks of the River Clough and explains the geology surrounding the Dent Fault in Garsdale. The fault took place some 290m years ago during the Hercynian orogeny and at this locality the rocks of the Lake District were uplifted by possibly as much as 2.5km above those of the Pennines. Adam Sedgwick was the first to discover and interpret this fault. Differences in structure along the river were very easy to see.

In the afternoon we went to Chapel-le-Dale and walked up to Great Douk Cave. Entry to the cave is down a tree-lined collapse and up a waterfall to get to the actual cave entrance. While most went down to view the bottom of the pothole we didn’t lose anyone actually going into the cave although we met a group of cavers who had obviously come out of another exit.

Very close to this there was a large expanse of limestone pavement. Pavements are formed when the limestone is first scoured by glaciers and fracturing occurs along bedding planes to give low level platforms on which boulder clay and wind-blown material was deposited as the glaciers retreated. Mildly acidic water then exploits the cracks and fissures in the rock. The characteristic clints and grikes form under relatively deep layers of soil with the soil gradually disappearing down the grikes and being eroded from the tops of the clints.

Sunday looked cloudier but still fine and dry and we set off for the Grassington Lead Mining Trail. Everybody seemed to have been visiting the centre of Grassington that day and the drive up through the village street (two-way, filled with pedestrians and narrower than many one-way streets) was an adventure on its own!

The trail was well laid out and generally easy to follow but it was clear to see what a desolate place the area would have been to work in. We saw archaeological evidence of mining from as early as the 14th century– lines of small shafts and mines showing the position of the ore vein as well as buildings from later on. The industry took off in the 18th and 19th centuries with a large number of people being employed and mines were at their most prosperous in the middle 19th century when dams were built and water brought in to drive pumps and new deep shafts were sunk. The Cupola smelt mill replaced several smaller mills and was fired by coal imported by canal from West Yorkshire; it originally had short horizontal flues but the flue was extended four times to prevent lead being lost in the vapour so that the final total length of flues was 1.7km.

Since 1880 there has been no serious attempt to re-open the mines although waste dumps were exploited for barytes and fluorspar in the last century.

After a well-earned rest after our morning’s excursion we then drove over to Giggleswick via a choice of routes; the main road or the ‘pretty route’ on minor roads past Malham Tarn and through the fantastic scenery of the fells; the latter also had the advantage of an ice cream van!

At Giggleswick we stopped at the side of the road to look at Giggleswick Scar which follows the line of the South Craven fault and is a good example of a major fault line scarp. There is a vertical displacement of 1.8km as evidenced by the juxtaposition of the Dinantian Great Scar Limestone with Namurian sandstone. The fault moved as recently as 1944 as recorded by an earth tremor in Settle.

Monday we left to go our separate ways. A few of us took the opportunity to visit Fauld Crator in Hanbury in Staffordshire. This is the is the of the largest explosion ever in Britain when, in 1944, 3670 tons of bombs, which had been stored underground in a disused gypsum mine, exploded creating a hole some 300 feet deep and a quarter of a mile in diameter. Amazingly, news did not leak out at the time.

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