The BGS Lexicon of Named Rock Units — Result Details

Lower Grinstead Clay

Computer Code: LGRC Preferred Map Code: LGrC
Status Code: Index Level
Age range: Valanginian Age (KV) — Valanginian Age (KV)
Lithological Description: The unit comprises soft grey to greenish grey mudstones and silty mudstones with subordinate thin beds of siltstone, clay ironstone, sandstone and limestone. In some areas, where the Cuckfield Stone Bed is absent, the upper and lower Grinstead Clay cannot be separated.
Definition of Lower Boundary: The base is taken at the up-section change from sandstone (Tunbridge Wells Sand Formation, Ardingley Sandstone Member, which may include at its top the Top Lower Tunbridge Wells Pebble Bed) to silty mudstones of the lower Grinstead Clay.
Definition of Upper Boundary: The upper boundary is taken at an up-section change from mudstones to sandstones of the (Cuckfield Stone Member). Where the Cuckfield Stone Bed is absent, the upper and lower Grinstead Clay cannot be separated.
Thickness: Up to 6.4m.
Geographical Limits: The unit is present in the Chailey area west to Cuckfield and northeast to between Kingscote and East Grinstead (Sheet 302). It extends onto the Tunbridge Wells sheet (303) where it crops out between East Grinstead and Tunbridge Wells and again near Danehill. In the Sevenoaks/Tonbridge district (sheet 287) the lower Grinstead Clay is seen along the southern margin of the sheet between Wicken and Oakfield and in the northeastern corner of sheet 318, north of the Lunce's Common Fault (north of Burgess Hill).
Parent Unit: Grinstead Clay Member (GRC)
Previous Name(s): none recorded or not applicable
Alternative Name(s): none recorded or not applicable
Stratotypes:
Reference Section  Philpotts Quarry, West Hoathly. The quarry exposes a "complete section of Lower Grinstead Clay ... and a frost-disturbed junction with the Cuckfield Stone". Bristow and Bazley (1972, p.35). 
Reference Section  Old Pit at Hillhouse Farm, in the Drewitts-Cuckfield area. Exposed the whole of the lower Grinstead Clay (6.15m); Gallois and Worssam (1993, p.49). 
Reference Section  Cuckfield Borehole No.1 TQ22NE/2 [TQ 2961 2731]. Full thickness of the unit encountered between 186.54 and 192.94m depth; Lake and Thurrell, 1974; Bristow and Bazley, 1972. 
Reference Section  Railway cutting, Sugworth Farm. Where 4.6m of the lower Grinstead Clay is exposed beneath the Cuckfield Stone bed; Gallois and Worssam (1993, p.48). 
Reference Section  Freshfield Lane Brickworks. The access road shows "a complete section of Lower Grinstead Clay, Cuckfield Stone and Upper Grinstead Clay". Bristow and Bazley (1972, p.35). 
Reference(s):
Bristow, C R and Bazley, R A. 1972. Geology of the country around Royal Tunbridge Wells. Memoir of the Geological Survey of Great Britain, sheet 303 (England and Wales). 
Gallois, R W and Worssam, B C. 1993. Geology of the country around Horsham. Memoir of the British Geological Survey, Sheet 302 (England and Wales). 130pp. 
Young, B and Lake, R D. 1988. Geology of the country around Brighton and Worthing. Memoir of the British Geological Survey, Sheet 318 and 333 (England and Wales). 
Dines, H G, Buchan, S and Bristow, C R. 1969. Geology of the country around Sevenoaks and Tonbridge. Memoir of the Geological Survey of Great Britain, Sheet 287 (England and Wales), 183pp. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E302 E303 E318 E333 E287