A Field Trip in Charnwood Forest

 

The Altar Stones Nature Reserve

Following on from a good exploration of Stannington in Sheffield, my next day out was with the Sheffield U3A Geology Group a few days later, to finally visit Charnwood Forest, which is a popular field trip location for by students of geology at all levels. 

 

The car park at Billa Barra Hill Nature Reserve

After two recces in March 2020, just before the COVID-19 Pandemic lockdown and then at the end of September 2021, a dozen members of the group met up at the Billa Barra Hill Nature Reserve car park on a rainy morning on the 20th of October 2021. 

 

An exposure of the Bradgate Formation on Billa Barra Hill

Making our way to the Charnwood Noon Column, where we had a quick look at the purple and green colouration of the volcaniclastic siltstone that has been used in the drystone wall here, we walked up Billa Barra Hill to see some small outcrops of the Bradgate Formation.

 

An exposure of the Bradgate Formation

Here, we noted the graded bedding and other sedimentary structures and had a good discussion about the rhomboidal pattern of jointing and very weak cleavage, which has been produced by the regional metamorphism of the Precambrian rocks in Charnwood Forest. 

 

A discussion of the Bradgate Formation on Billa Barra Hill

Out next stop was the old quarry that had been excavated in the side of Billa Barra Hill, the access to which down some steep steps were of some concern during the recces, particularly because we try to accommodate the physical abilities of the members of the group as a whole – most of whom are in their 70’s. 

 

Inspecting slickensides at Billa Barra Hill

The main point of interest at this location are the slickensides that are exposed along the plane of a fault, which is quite unusual in that it is not oriented vertically but horizontally. Our eldest member Pauline, who is in her 80’s but still capable, negotiated the steps without difficulty and we returned to the car park and drove to the Altar Stones Nature Reserve. 

 

The Bradgate Formation at the Altar Stones Nature Reserve

By this time, the weather had improved considerably and, after having a preliminary walk around the reserve to observe the numerous outcrops of jagged rocks along the ridge, which dip steeply to the south-west, we took advantage of the welcome break in the weather to have a slightly early lunch and enjoy the views of the surrounding countryside. 

 

The Bradgate Formation at the Altar Stones Nature Reserve

From our earlier visits, Paul May and I decided that this site would be the main focus or our geological investigations and, after finishing our lunch, we had a much closer look at the Bradgate Formation, the Sliding Slump Breccia, the Beacon Hill Formation and the Park Breccia.

 

Negotiating a path at the Altar Stones Nature Reserve

During the recces, the weather had been overcast and the features of the rocks were not particularly easy to identify; however, in the sunshine, once everyone had got their eye in, we could see a wide variety of colours and textures that distinguish these various rock formations. 

 

The Sliding Slump Breccia at the Altar Stones Nature Reserve

Having had a good look at these volcaniclastic rocks, we returned to the cars and drove the short distance to the Hill Hole Nature Reserve car park, from which there is a short walk to the exposures of the distinctive pink and green coloured diorite, which was named markefieldite after the village of Markfield and was very widely used for the top bed of ballast upon which railway tracks are laid. 

 

Examining markfieldite at Hill Hole Nature Reserve

 

We finished another good day out by walking down into Markfield, where we had a look at the markfieldite used in the exterior of the Church of St. Michael and All Angels and the Swithland slate headstones, before having a leisurely wander around the village to see examples of the vernacular architecture. 

 

Walking around Markfield