The Geology Along Totley Brook

 

A small waterfall

When preparing the 2023 field trip itinerary for the Sheffield U3A Geology Group, one of the members suggested that we could have a walk around Totley, where she lives, but the consensus was that there probably wouldn’t be enough to fill the day, which usually starts at 10:30 and finishes by 15:30. 

 

The Ordnance Survey map of Totley

 

I had only briefly visited the area around All Saints church and, having plotted a route using the Ordnance Survey map, a few days after my walk from Fulwood Road to Sheffield General Cemetery, I spent a couple of hours exploring Totley Brook. 

 

A dry stone wall built with Greenmoor Rock

Alighting from the No. 97 bus from Sheffield at its terminus on Baslow Road, where I immediate found the entrance to Gillfield Wood and followed the public footpath, which runs along the northern slope of quite a substantial valley, until I reached a dry stone wall. 

 

The geology around Totley

 

The geological map shows that Totley Brook cuts through the Greenmoor Rock, which in this part of Sheffield is split by thick partings of mudstone or siltstone. I didn’t get near to inspect it very closely, but its thin bedding and colour are quite characteristic features of this rock formation. 

 

Flaggy Greenmoor Rock in the streambed

 

Eventually I caught sight of the brook and, when the path dropped down to a lower level, I could see blocks of flaggy sandstone littering the streambed. I noted plenty of unstratified head but there was no sign of outcrops until I encountered a couple of meanders, where small outcrops of flaggy sandstone are exposed in the bank, but I could not get access to them. 

 

An exposure of Greenmoor Rock in a meander of the brook

 

With the brook continually meandering and with no GPS device or obvious landmarks to pinpoint my exact location along the brook, I continued to see flaggy sandstone blocks littering the streambed, which I think must be Greenmoor Rock but didn’t note any further outcrops.

 

Another meander littered with slabs of Greenmoor Rock

 

The first recognisable landmark was a signpost at the junction of the public footpaths to Mickley Lane and Woodthorpe Hall, which I was able to identify on the Building Stones Database for England map explorer. This shows that I had by now crossed a fault with a downthrow to the east and that, for the rest of my walk, Totley Brook flowed across the Grenoside Sandstone or the associated Pennine Lower Coal Measures Formation PLCMF) strata. 

 

The Building Stones Database for England map explorer

 

Continuing along the path, in the stream banks I could see mudstone that is weathered to yellow/orange clay, with a thick covering of head and sometimes alluvium, which had been deposited in times of flood and, wherever possible, I got down into the streambed to investigate them further. 

 

Views of the stream banks

As I headed further downstream, exposures of thinly bedded sandstone, siltstone and mudstone are more frequently encountered in the streambed and stream banks. At one place that I can’t precisely locate, a thinly bedded sandstone forms quite a substantial outcrop in the streambed, with forms distinct riffles. 

 

An outcrop of rock in the streambed

 

Immediately downstream, slabs of a slightly more massive fine grained sandstone project from the stream, which appear to be dipping to the south-east. Before I had crossed the fault, the geological map shows a dip of 20 degrees to the north. 

 

Steeply dipping slabs of sandstone

 

On the Friends of Gillfield Wood website, a geological map produced by Bob Warburton for his thesis shows that, before arriving at the previously described fault, several measurements show that the strata dip to the north but beyond this the dip is quite variable, with measured dips to the north-east and south-east reflecting the proximity of the Dronfield Syncline. 

 

A geological map of Gillfield Wood © Bob Warburton

A little further downstream, the strata changes again to a much more thinly bedded sandstone, with softer beds being differentially weathered. Along this stretch of the brook, where the sandstone is slightly more massive and the beds are thicker, there are small waterfalls. 

 

Thinly bedded fine grained sandstone in the streambed

 

From this point onwards, the brook continues to meander across PLCMF strata and the Grenoside Sandstone, in a much wider and shallower valley, with mudstone and head exposed in its banks. Reaching the path to Mickley Lane and crossing the bridge over the brook, there is an exposure of what is probably Grenoside sandstone, but I couldn’t get close to it. 

 

A view from the bridge on the path to Mickley Lane

On my walk, although I had seen plenty of Greenmoor Rock as small slabs in the streambed and occasionally in the stream bank, I did not obtain any samples and those that I collected were all from exposures where the PLCMF or Grenoside Sandstone form the underlying rock. 

 

Specimens collected during the walk

 

They vary from grey to buff in colour with varying degrees of iron content and staining, are fine to very fine grained in texture and mostly thinly bedded. The specimen that I collected from near to the waterfall is grey in colour, very fine grained and  micaceous - a characteristic of the Grenoside Sandstone - but none of the specimens look much like the rock that I have seen where used as a building stone in the type locality of Grenoside. 

 

Very fine grained grey micaceous sandstone