A Geological Recce at Creswell Crags

 

Various cave entrances at the west end of Creswell Crags

 

After gathering enough information and taking enough photographs to illustrate A Geology Lesson at Waverley, for the Wave magazine, I quickly wrote my short article and spent the rest of March preparing for my “Let’s talk about the stones” walk at Boston Park and Moorgate Cemetery. 

 

A view from the east end of the lake

 

With this being successfully completed on the first weekend of April, the onset of a typical April showers weather pattern restricted my outdoor activities – except for another brief trip to Waverley with my next door neighbour Dan - and my next day out was to Creswell Crags, to provide geological input on a recce by Dave for the next Sheffield U3A Geology Group field trip. 

 

The Anston Stones Wood Geological Trail

 

I had visited Creswell Crags back in 2015, to meet the manager and to discuss the possibility of writing a guide to the geology of the gorge, along with my friend Mike who had co-written the Anston Stones Wood Geological Trail. We were given a free tour of the Church Hole Cave, where the rock art can be seen, which lasted just over half an hour but, except for the ibis, I thought that most of what was shown to us by the guide looked like natural features of the dolomitic limestone. 

 

The ibis

 

When this was proposed for the field trip itinerary, I emphasised the need to combine this with other sites in the area, such as Pleasley Vale and Robin Hood’s Cave but, very soon after meeting a member of staff at the visitor centre, it became obvious that Dave intended the group to spend the whole day there. At this point, I decided that I would show Dave the features that I thought were of interest, while we walked around the lake, but I would not be joining the group on the field trip. 

 

A view along the south side of the lake at Creswell Crags

 

Leaving the visitor centre and stopping at the east end of the lake, we stopped to look at the very distinctive buttress like features that are formed on its southern side. The gorge, which is cut into the upper Sprotbrough Member of the Cadeby Formation, is traversed by inclined joints that divide the buttress like features and in many places have been widened into caves. 

 

Undercutting at the base of the limestone outcrop

The geological memoir describes the crags as comprising about 18 metres of hard massive limestone that is crystalline and granular and contains many stylolites. Although the memoir does not mention it here, the lowest 2 metres are composed of pseudobreccia, which has resulted in undercutting and the entrances to some of the caves coincide with these beds. 

 

A view along the south side of Creswell Crags

 

There is well pronounced large scale cross-bedding at the east end, especially in the lower part of the crags, which the group has previously encountered during field trips to the Don Gorge, Warmsworth and Clowne. Cavities of various sizes are also very common, but I did not see many that are in the form of crystal lined vughs. 

 

Iron staining on a rock face

 

When first visiting Creswell Crags, in one of the rock faces that are set back from the lake, I vividly remember the iron staining that covers part of the joint plane and has been presumably washed down from a bed of red marl that occurs within the Sprotbrough Member or from the overlying Edlington Formation. 

 

A buttress like feature on the south side

 

In Braithwell, Stainton and Micklebring on the Doncaster/Rotherham border, a red ochre known as ruddle/raddle was mined from the Cadeby Formation that, amongst other uses, was used by farmers to mark their sheep. I know next to nothing about cave art, but the Cave of Altamira in Spain came to mind, where similar ochreous compounds were presumably used and I have wondered if the inhabitants of the caves at Creswell Crags ever thought about making use of this. 

 

A view of the north side of Creswell Crags

 

The caves at Creswell Crags have long since had their internationally significant Quaternary sediments and fossils removed and, with all of the 9 major caves gated and inaccessible - except Church Hole and Robin Hood for tours - and much of the rock faces thickly overgrown, the geological features aren’t that easy to see. 

 

A small cave with a sand filled fissure

 

Looking closely, in places it is possible to see that some of the fissures are filled with sandy deposits, which very often contain Quaternary mammal fossils. Also, in one place on the north side of the lake, I noted solution hollows, which I seen once before in the Magnesian Limestone at Warmsworth Park, when undertaking a survey for the Doncaster Geodiversity Assessment. 

 

Solution hollows

 

As at Anston Stones Wood and other gorges in the Magnesian Limestone escarpment, Creswell Crags is believed to have been formed by glacial meltwater flowing from an ice sheet to the west. When returning to the car park and looking across the field to the tip of waste material from the Steetley dolomite quarry, I noticed that the soil was full of quartzite and sandstone pebbles, which are remnants of much more extensive glaciofluvial deposits that once covered much of the Magnesian Limestone.

A few across a field strewn with glaciofluvial pebbles