Geology in Anston Stones Wood - Part 2

Dolomitic limestone crags in Anston Stones Wood

 

I have visited Anston Stones Wood several times, to undertake surveys, lead various groups and to take photographs to illustrate talks or for various publications and during my last walk, to further explore its geology, I was very surprised to see so many clearly visible exposures of the sandstone known as the Mexborough Rock.

 

A stream bank exposure of Mexborough Rock

Although I have no evidence, based on systematic recording of its condition over the years, I did think that there was something different to when I last surveyed the area in detail back in 2000. I found only an occasional outcrop of Mexborough Rock then and I wondered if the extended periods of wet weather in 2007 and 2019 had resulted in significant erosion of the banks of Anston Brook, thereby exposing more of the bedrock here.

 

A slumped block of limestone

Carrying along the path, which then rises up towards the dolomitic limestone crags that are exposed in the south side of the gorge here, I was particularly interested to see a very large slumped block of limestone that has become detached from the main outcrop by cambering – a process that frequently occurred in periglacial environments during the Quaternary Period.

 

An easily accessible outcrop of dolomitic limestone

I didn’t stop to further investigate this very interesting exposure of the Cadeby Formation, which I had first encountered back in 1997 and have examined a few times since, but the overhang here has an excellent example of flowstone that links the rock face to a detached block.

An overhang in the dolomitic limestone crags

This outcrop is now well known to the Sheffield U3A and various other geology groups and is also frequented by boulderers, who like to climb the the various rock faces that can be found along the length of this limestone gorge.

 

A flight of steps on the main footpath

Walking down a flight of steps, which I don't recall seeing before, I stopped on the bridge over the brook – which is again built with Staffordshire Blue engineering bricks, with the upper section over the arch rebuilt using another unknown variety of brick.

 

A bridge over Anston Brook

From this vantage point, I could clearly see further examples of flaggy Mexborough Rock in the stream banks and below the waterline. I didn’t get close up to examine it closely or take a sample but, judging by the colour of the soil, this is the variety known as Rotherham Red sandstone.

 

Flaggy Mexborough Rock below the waterline

Rotherham Red sandstone is typically a massive, medium grained sandstone that frequently contains well developed cross-bedding, which can be quite large in scale; however, at Boston Park and Canklow Woods in Rotherham, there are also similar cross-laminated flaggy varieties overlying the massive beds.

 

A detail of cross-laminated Mexborough Rock