Friday, 18 June 2021

A Field Trip in Conisbrough - Part 2

A bryozoan reef at North Cliff Quarry

As one of the field trip leaders of the Sheffield U3A Geology Group, reflecting my working background in the building restoration industry in London and specialist interests in building stones, many of the days out that I have organised have had an ‘urban geology’ theme – in Leeds, Sheffield and Pontefract.
Building in Stone - Information for Teachers
The English Heritage Information for Teachers leaflet, Building in Stone, which I co-wrote with the Education Officer at York in 2002, was strongly influenced by my experiences of visiting many of the castles in their care. These include Conisbrough, Peveril and Bolsover castles, which were built to take full advantage of prominent landforms that overlooked long established trade and communication routes.
With considerable experience of geological conservation, however, in South Yorkshire, the Peak District National Park and the Republic of Ireland, I have also encountered various geological sites with particular educational value, with the next stop on my ‘field trip’ being one of these – at North Cliff Quarry, which is 700 metres to the north-west of St. Peter’s church in Conisbrough.

The route from Wellgate to North Cliff Quarry
Taking the path at the end of Wellgate, which leads towards Conisbrough railway station, and then following the path along the northern boundary of the school playing fields, there are good views of Conisbrough Viaduct to the west, which marks the beginning of the Don Gorge.
Conisbrough Viaduct

Looking to the north, there are also good panoramic views of the Magnesian Limestone escarpment on the north side of the valley formed by the River Don, which stretches into the distance towards High Melton and Hickleton.
A panoramic view of the Magnesian Limestone escarpment

Arriving at the south-west corner of North Cliff Quarry, which sits on the edge of a faulted escarpment of the Cadeby Formation known locally as The Crags, I skirted the quarry along the path that continues around to its north side, before descending along a path into the quarry floor.
A general view of North Cliff Quarry

Health and Safety considerations are now paramount when organising field trips, with ‘risk assessments’ now being required by the leaders at the Sheffield U3A Geology Group. Usually, this just requires common sense and, during their field trip, the group of Year 7 KS3 students from the newly formed XP School in Doncaster took great care when navigating their way around the quarry, which has rocks hidden under long grass and bottles and cans left by inconsiderate youths.
The bryozoan reef and massive limestone
The principal feature of interest here is the bryozoan reef in the Wetherby Member of the Cadeby Formation, which forms a pillow like irregular and unbedded mass in the north-east corner of the quarry. Lookig closely, it can be seen that the thick massive beds of dolomitic limestone have been depressed by the weight of the overlying reef, when the sediment was still soft.
Massive bedded limestone at North Cliff Quarry

As with very many sites that I identified in South Yorkshire as having good educational value, the rock faces are slowly being obscured by shrubs and trees. Although the dumping of burnt out cars no longer seems to be a problem, Doncaster MBC do not maintain these sites and, like other local authorities in South Yorkshire, rely on the voluntary efforts of the mainly retired members of the Sheffield Area Geology Trust.
Cross-bedded limestone with bivalves

With a bit of care, however, it is still possible to get close up to the rock faces to examine some of the ooidal, cross-bedded massive beds, which are and packed full of shells of the diminutive bivalve Bakevellia antiqua that can be seen with the naked eye.
Massive bedded limestone

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