Geoconservation of the Kenilworth Sandstone at Castle Hill Quarry (17/05/25)

Report by Jane Allum

A group of 13^[1] keen and spritely volunteers, led by Jane Allum, met at the Castle car park and walked down the private road to access Castle Hill quarry just off Grounds Farm Lane, a short distance beyond the castle visitor centre. A beautiful 21^oC sunny day had unfolded and the conservation party was ready to get started. The preferred access into the quarry is very steep but Larry cleared the entrance path and dug a handy step for us to enter safely (Figure 1). Ian Fenwick joined the group later in the afternoon and braved the barbed wire access point at the eastern end of the quarry, which we do not recommend. Stuart Burley had arrived earlier in the day to clear some of the nettles that had overgrown the quarry since the February recce so that once the party was in the quarry movement was relatively easy. Jane had consulted with the Warwickshire Wildlife Trust to assess the environmental impact of our geoconservation.

---

^[1] Mel Dearing, Gill Chant, Andrew Sanderson, Mihaela Bokor, Tony Smith, Brenda Watts, Larry Wooding, Lousie Grew, Trevor Howard,  Ian Fenwick, Stuart Burley and Peter Hawksworth.

Castle Hill Quarry is located close to the western extent of the Kenilworth Sandstone, a short distance from the Western Boundary Fault of the Coventry Horst (Figure 2), although the fault has no topographic surface expression. The quarry was worked into the uppermost part of the Kenilworth Sandstone Formation sequence – immediately to the south, basal mudstones of the Ashow Formation are mapped by the BGS (Figure 2).

There are three exposed faces in the quarry which we estimate provide a total of around 7m of stratigraphic section. The base of the face at the eastern end of the quarry has evidence of an active badger sett so no work was undertaken within 10 m of this face. Once in the quarry the conservation party split into two groups. One group worked on the so-called breccia beds in the southern part of the quarry whilst the second group focused on the flat bedded upper sandstones at the north-western end of quarry.

The geoconservation party worked hard for around 2 hours. At the end of conservation activity the quarry faces were superbly exposed. We then used the WGCG portable jet wash to remove lichen, moss and grime from the faces (Figures 3 and 4). Talus was removed from the base of the faces whilst hand brushing was initially used to remove ivy, moss and loose soil from the exposed faces.

Ian Fenwick, who was involved in the archaeological surveying of the quarry a few years ago, related the anecdotal tale that the quarry was used for 12^th and possibly 15^th century repairs to the castle. Indeed, Kenilworth Castle has a long history of construction, rebuilding and extension from the 11th Century to the 16^th Century with several areas of excavation clearly still visible in LiDAR images of Kenilworth (Figure 5). The quarry is located ~600m south of the castle but only ~200m from the embankments and outer walls of the military enclosure development. The archaeological quantity surveyor calculated that the volume of sandstone removed from the quarry was sufficient to construct most of the outer walls of the castle. Although it is not possible to establish the period when the quarry was worked it seems plausible that it was used for the later rebuilding and outer walls.

Although of mediaeval origin, the southern side of the quarry has clearly been used for early 20th Century fly tipping with ashy sand lining the side and floor of the quarry containing broken ceramics, an oyster shell (oysters being the food of the poor in the past) and numerous glass bottles. Figure 7 shows and example of a glass bottle in excellent condition which was manufactured by the Leamington Spa Aerated Water Company.

Now that we have cleared the quarry of much vegetation and cleaned exposed faces much work will be undertaken to record the sequence of sandstones in the quarry, collect information on palaeocurrent directions and the pebble content of the so-called breccia beds. The Kenilworth Sandstone Formation is considered to be Permian in age, which spans ~50 million years, from the end of the Carboniferous Period 300 million years ago (Mya), to the beginning of the Triassic Period 252 Mya. Castle Hill Quarry exposes a sequence of cross-bedded and high energy plane-bedded sandstones in addition to the angular pebble conglomerates.  At this time there was a mountain band to the south of the Midlands which had formed as Pangea was created. This event called the Variscan Orogeny created the Variscan mountain belt, which includes the mountains of western Spain, southwest Ireland, Cornwall, Devon, Pembrokeshire, the Gower Peninsula and the Vale of Glamorgan. There are several units of pebbly sandstones in the Kenilworth Sandstone sequence which are called ‘breccias’. They are actually angular pebble and cobble conglomerates which are water lain deposits, their angular nature suggesting they have not travelled far. The clasts include PreCambrian lavas, Cambrian quartzites and Carboniferous chert which was used by Fred Shotten in 1929 to suggest that they were derived from the west, inferring a highland area as close as the Lickey Hills.

Now that we have very clean quarry faces, the task of better understanding these fascinating sediments is much easier (Figure 8). Field trips to Castle quarry and other related Kenilworth Sandstone outcrops will be organised by the group to explore how they were deposited and unravel their source provenance.

It should be noted that F. W. Shotton, FRS, Professor of Geology at the University of Sheffield 1945–1949, and at Birmingham 1949–1974 was involved in the early interest here which led WGCG to seek its SSSI designation.

Thanks to everyone who gave up part of their weekend to participate in the clean-up and worked hard to such great effect. An excellent job very well done!