Situated to the west of the Malvern Hills, Brockhill Quarry was cleared by EHT volunteers on the 30th October 2023. In this post, we summarise the geology of this interesting site and discuss the clearance completed. Understanding of the local rocks, flora and fauna at this site has helped the group target their work and ensure that all clearance completed is sensitive to both geo- and biodiversity.

By Dick Bryant and Peter Bridges.

Brockhill Quarry (Grid Reference SO 636 439) lies to the west of the Malvern Hills, some 300m north of Brockhill Farm off Mathon Road. It is bounded to the north by the Public Bridleway from Mathon Road to Brockhill Road and the stream flowing from the Purlieu to Cradley Brook. Its western boundary is the large bend in Mathon Road and the southern is the field boundary with Brockhill Farm.

The local geological setting is shown in Fig. 1 below. A sketch map of the quarry (Fig. 2) shows its main features. The quarry is located within the upper part of the marine Silurian rocks which locally are represented by the following (Table 1):

Table 1. Geology summary.

Figure 1. A geological map of the area around Brockhill Quarry (BGS).

True North is towards the top of Fig. 1 – as shown by the black arrow. Brockhill Quarry is located at the red star.

From east to west, the light purple horizon underlying Brockhill Road is the outcrop of the Lower Ludlow Shales (LLS). To the west, the blue N-S trending band to the east of Brockhill Quarry and above the LLS is the Aymestry Limestone which is overlain by the Upper Ludlow Shales (ULS) (light blue). The ULS is well-exposed in the 3-5 metre high, south face of Brockhill quarry, the eastern part of which follows and is controlled by a prominent, east-west striking joint or fault plane – see Figs. 1 (above) and 2 (below). A fault with the same orientation is shown displacing the Aymestry Limestone in Fig. 1 above.

Several authors have described the occurrence of calcareous sandstones with limestones and thin shale interbeds within the ULS and have noted some bedding planes showing concentrations of shell fragments and ripple bedding; the shell-rich horizons having been created by shallow-water currents washing away the finer-grains, leaving residual shell-rich layers.

The Downton Castle Sandstone (DCS) (the thin beige-coloured outcrop on the map trending north-south) is exposed in the western part of Brockhill quarry and overlies the Upper Ludlow Shales. This marks a change in sedimentation from shallow-water marine to a littoral marine sand complex and/or a storm-deposited shelf sand – the start of the Old Red Sandstone facies in the younger Pridoli Series of the Upper Silurian. At the base of the DCS this transition is marked by the Ludlow Bone Bed (LBB) – a very thin 0.6 to 2.5 cm thick horizon which contains fish remains, fish scales, some brachiopods and phosphatic nodules. Phipps (1955) described the Ludlow Bone Bed as having “been considerably attacked through the years”.

Barclay (1997) described the beds of the DCS at Brockhill Quarry above the LBB as “buff, fine-grained, micaceous sandstones, sandy shales and shales with plant remains”. The subcrop of the Raglan Mudstone Formation (light purple) to the west of the B4232 makes up the western part of Figure 1 above.

Figure 2. A sketch map of Brockhill Quarry showing its main features.

Figure 3 below is a photograph of the line A to B on the sketch map and is the joint or, more probably, fault-controlled, south wall of the quarry with a near-continuous exposure of over 30 m of Upper Ludlow Shales. As in most of the quarry the hard rock face of the shales is capped by 0.5 to 1 metre of head – broken, angular fragments of local country rock held in a finer-grained, unconsolidated matrix of similar provenance. Various processes have been involved in the formation of this horizon – soil creep, solifluction, etc. The head deposit forms a near-continuous cover over the local area.

The area around points B and C is the transition between the Upper Ludlow Shales and the Downton Castle Sandstone. This is where the outcrop of the Ludlow Bone Bed would be expected but unfortunately, despite our best efforts, Phipp’s comment above held true and no conclusive evidence of the LBB was found during this clearance exercise.

Area C to D is the area with the best exposure of the Downton Castle Sandstone in the quarry. Various features are seen including an enigmatic outcrop of nodular sandstone near D. Area E is heavily overgrown with numerous fallen trees and evidence of backfill with local rock but also some landfill. No clearance work was undertaken here. Clearance work was concentrated on three contiguous areas – A to B, B to C and C to D.

The text and images below describe the work completed and show the sites before and after clearance.

Figure 3. The south wall of Brockhill Quarry before clearance.

Clearance work took place in stages. Stage 1 work entailed removing fallen timber and cutting back any overhanging vegetation obscuring the outcrop and removing it to one of the areas delineated as “overgrown” in Figure 3 where it was left to rot down – providing some shelter to smaller wildlife. Where bedrock was covered by scree and other debris this was cleared with mattocks and spades and the newly exposed surfaces cleaned using heavy-duty nylon brushes, wire brushes or trowels.

Figure 4. The same view as Figure 3 on completion of Stage 1.

Figure 5. A close-up of an Upper Ludlow shale outcrop on the south wall on completion of Stage 1.

In Stage 2, the cleared area which is still covered was sprayed with a dilute solution of sodium percarbonate – a mild, eco-friendly bleach which as it breaks down oxidises, attacks and breaks the fine filaments which attach mosses and lichens to the rock surfaces thus helping to remove the moss and lichens left remaining after Stage 1.

Figure 6. Part of the same south wall outcrop on completion of Stage 2.

All the by-products from the breakdown of the sodium percarbonate are completely harmless – simply water, oxygen and sodium carbonate (washing soda). A comparison between Figures 5 and 6 above shows how removal of moss and lichens improves the appearance of the rock face dramatically, almost returning the exposure to the fresh rock surface seen when it was first quarried and allowing a detailed examination of the geology of the renovated rock face, which would have been impossible without a clearance programme described above.

Figure 7. The area around B and C on the sketch map (Fig 2) before clearance.

Figure 8. The same area after clearance.

As this area was the transition zone between the Upper Ludlow Shales and the Downton Castle Sandstone (DCS) care was taken not to destroy any traces of the thin and friable Ludlow Bone Bed (LBB) at the base of the DCS, however, as mentioned above, no traces of the LBB were found.

The Brockhill clearance exercise described above is typical of those undertaken under the annual EHT Geosite Clearance programme, which is documented in more general terms in a second post here. Similar clearance exercises in the 2023/24 programme are planned for Middle Hollybush Quarry or Westminster Bank Quarry, North & Tank Quarries and an area south of County Quarry. New volunteers are welcome; please contact Peter Bridges at ptrbrdgs@gmail.com.