Field Trip to Hill Farm, Maxstoke & Corley Rocks – 19/8/23 by Mike Allen

This excursion examines two sites offering perhaps the best exposures of the late Carboniferous Red-Beds of the “Warwickshire Group” currently available in the north of the county. They are located on opposite sides of the Warwickshire Coalfield (an uplifted area known as the Coventry Horst) and both display outcrops of current-bedded sandstone delivered by large rivers flowing from a mountain chain, raised up to the south during the Variscan Orogeny, flowing towards the Pennine Coal Basin. Careful inspection reveals contrasting sediment sources much argued and debated for over a century without any final consensus emerging yet!

Fig 1 – geological sketch map

This site at Hill Farm is located very close to the Western Boundary Fault of the coalfield, and shows the Arley conglomerate bed in the foreground (peeping through the grass!) dipping towards and under the sandstone face of an old quarry in the background. The constituent pebbles of this conglomerate include pieces of chert derived from Carboniferous Limestone and are generally thought to derive from a western source, also suggested by the predominant current direction seen in the cross-bedded sandstones in the quarry.

Fig 2 Hill Farm exposure
Fig 3 View west from Maxstoke to the Dudley Hills…..Rowley Regis, Castle Hill and Wren’s Nest Hill

Nearby, one can stand at the top of a low, but prominent, escarpment formed by erosion along the boundary fault. The views westwards across the younger Triassic beds of the Knowle Basin extend to the West Midland conurbation, with the hills of Lickey, Rowley and Dudley all featured, as well as the more obvious skyline of Birmingham city centre.

Fig 4 Corley Rocks

These more impressive outcrops at Corley Rocks consist of slightly younger sandstones with pebble beds, mudstone layers and various types of cross-bedding. A few of the pebbles contain fossil shells which point to a Silurian origin, and current directions suggest a contrasting eastern source (Fig. 1).

Fig 5 Corley Rocks

This location lies towards the eastern boundary of the coalfield block and views nearby take in former colliery sites working the productive Coal Measures which underlie the unproductive Red- Beds. On the horizon is the Nuneaton Ridge formed by steeply upturned rocks of much greater, Pre-Cambrian to Ordovician, age.