A Geology Field Trip in Ashover

 

Galena

After my walk around the industrial east end of Sheffield, where I learned about its history of steel making and had a good look at the Ketton stone used in the former Thos. W. Ward premises, my next day out was with the Sheffield U3A Geology Group to Ashover. 

 

Ashover Rock

Meeting at the layby on Alton Lane, we started the day by having a quick look at Ashover Rock, known locally as the Fabrick, which had been the last place that we had visited on the recce a couple of weeks earlier. 

 

A view across Ashover from Ashover Rock

Our leader for the day Dave, a retired civil engineer, had visited Ashover on two further occasions to prepare the walk and he proceeded to introduce the Group to the geology of the area, including the Ashover anticline. Adding comments on the geology as required, I hovered around in the background to take photographs that might be used for the report on the day.

 

A geological cross-section of the Ashover anticline

Returning to the cars and parking at a convenient place in Ashover, we then had a very quick look inside All Saints church, noting the very rare Norman lead covered font, before heading down to the River Amber. Due to issues with the owners denying access, Dave had decided not to visit Butts Quarry and we carried on up the west side of the valley, which had exposures of the Fallgate Volcanic Formation in places. 

 

A path on the Fallgate Volcanic Formation

 

Taking a bit of a roundabout route along various public footpaths above the crags formed by the Eyam Limestone Formation, we had views of the grassland formed on the Bowland Shale Formation, where poorly drained ground was marked by an abundance of bog loving plants and above which rose a wooded escarpment of Ashover Grit. 

 

Grassland on the Bowland Shale Formation

We then made our way to the site of the former Gregory lead mine, which was one of the most productive in England during the C18, before it was closed in 1803 after working for 250 years. I would have liked to have spent a little longer looking through the spoil heap, especially since one of our group found a good specimen of what we thought was sphalerite. 

 

The spoil heap of the Gregory mine

Continuing on a route that we had not followed on the recce, we were led down past the Grade II Listed Ravensnest chimney – part of the engine house at the Gregory mine - to Overton Hall, where we had lunch and I took a few photos for the British Listed Buildings website. 

 

Overton Hall

Walking down past Milltown Quarry and old lead rakes, our next stop was Jetting Street, where we had a good look at the highly weathered pale turquoise coloured toadstone clay, which had orange stained inclusions in places. 

 

Toadstone clay

Removing one of these with my Estwing hammer, I was surprised to discover that it was rounded and slightly elongated and much harder than the clay that it was embedded in, which suggested that the inclusions could be lapilli. 

 

A lapillus in toadstone clay

 

After a year of it being stored in a sample bag, the specimen has dried out and started to exfoliate. Examining the fine orange sand like debris in the bag, there is an abundance of elongate colourless/off white crystals, which I think are plagioclase feldspars that have not been weathered – unlike the ferromagnesian minerals.

 

Exfoliation on the lapillus

Making our way to our last site at Hockley lime kilns, we passed by Fall Mill and, after talking with the owners, we were all invited into the building – now converted into a house - to see the internal mechanism of the water wheel, which would once have been linked to a grindstone but is now a feature in the kitchen. 

 

The interior of Fall Mill

 

At Hockley lime kiln, we inspected the green and purple tuff and noted the many calcite veins that criss-cross the exposure. In the various guide books that we had referred too, the exposures of tuff in the cutting to Hockley Quarry, which we did not visit, are recorded as containing lapilli and pumice but we did not see these. 

 

Hockley lime kilns

During our walk, we had passed by a couple of old limestone quarries and seen a small outcrop of the Monsal Dale Limestone Formation next to the lime kiln at Jetting Street but, quite surprisingly, we had not had a good look at the Carboniferous Limestone, which include the knoll reefs in the Eyam Limestone Formation that form crags on the west side of the valley. 

 

Knoll reefs in the Eyam Limestone Formation

Arriving back in Ashover, at the end of a 6 km on what had turned out to be a very warm day, we then convened at the Old Poets Corner public house where, as on the recce two weeks earlier, the pint of Everards Tiger was very welcome.

 

The Old Poets Corner