The Geology of Shirtcliff Wood - Part 2

 

An ochreous seepage in Shirtcliff Brook

Carrying on down Stradbroke Road, during my walk from Normanton Hill to Treeton, I crossed over the A57 and then walked northwards along the public footpath until I reached the end of the modern housing estate, which lies on the south side of Shirtcliff Brook.

 

The escarpment of Woodhouse Rock

Stopping briefly to look at the escarpment of Woodhouse Rock, which forms the north side of the Shirtcliffe Valley, and the tower and steeple of St. Mary’s church in the distance, I dropped down into the valley and followed the path into Shirtcliff Wood.

 

Yellow clay exposed in the stream bank

With most of the undergrowth having died back, I could get much closer to the stream bank than during my visit the previous summer and was therefore able to see beds of mudstone and yellow clay, which I hadn’t previously noted.

 

Mudstone exposed in the stream bank

Shirtcliff Wood, Smelter Wood, Bowden Housteads Wood, the Shire Brook Valley and the Waverley Estate – which I had explored during the first summer of the COVID-19 Pandemic - are all set on strata from the Pennine Middle Coal Measures Formation and, except for ganister, I had by now encountered all of its typical rocks.

 

Tree roots exposed in the stream bank

Following Shirtcliff Brook down to a stretch that is notable for the tree roots exposed in its steep sided banks, I was very surprised to discover a small exposure of what I think must be a former streambed – left behind when the brook changed course in geologically recent times.

 

An exposure of a former streambed

Looking closely, it comprises a section of flat, angular stones that are alternately oxidised (orange) and reduced (grey), which are similar in size and shape to those that lie in the streambed immediately beneath it, and which passes into the dark silt above it.

 

A detail of the former streambed

 

A little further downstream, I then discovered another outcrop of the Woodhouse Rock, where the topset beds were clearly visible in a prominent exposure of more massive sandstone, which I had also never noticed before.

 

An exposure of sandstone

Proceeding further downhill, there are further examples of moderately thick beds of flaggy sandstone exposed in the streambed and, looking down on the bedding plane, the pattern of jointing can be clearly seen.

 

Jointing in flaggy sandstone exposed in the streambed

Further along the course of Shirtcliff Brook, there is evidence of the drift mining of the Swallow Wood coal seam, which was also exploited at a few other places in this valley, but there are no exposures of rock or coal visible.

An area of woodland affected by drift mining

There is evidence of the presence of coal in the area, however, in the form of the bright orange ochreous deposits in the stream banks, which are the product of the oxidation of the mineral pyrite that often occurs in the coal seams.

 

Ochreous deposits in the stream bank

In the 45 minutes that I spent wandering along Shirtcliff Brook, I found enough exposures of a wide variety of rocks to be able to provide a good introduction to the Coal Measures strata and, including the coal at Smelter Wood and the sandstone quarry along The Edge, it would make a good half day field trip for the Sheffield U3A Geology Group.

An exposure of flaggy sandstone