The BGS Lexicon of Named Rock Units — Result Details

Horsham Stone Member

Computer Code: HST Preferred Map Code: HSt
Status Code: Full
Age range: Hauterivian Age (KH) — Hauterivian Age (KH)
Lithological Description: Sandstone, calcareous, generally fine-grained, micaceous, locally well laminated, pale grey to greenish/olive grey. Contains clayey partings and lignite fragments and rootlet traces. Frequently shows internal slumping and deformation. Informally subdivided by an interposed mudstone, south of Christ's Hospital [TQ 148 285] in the Horsham area.
Definition of Lower Boundary: The base is conformable at the change from mudstones and silty mudstone of the lowest part of the Weald Clay Formation into the fine-grained calcareous sandstone of the Horsham Stone. This horizon is known to be closely underlain by a significant but unnamed clay ironstone seam. Within the Warninglid Borehole TQ22NW/1 [TQ 2488 2701] this change is marked by the change from greenish grey mudstone up into ripple marked sandstone with lignite laminae and mud-flake conglomerate.
Definition of Upper Boundary: The top is conformable at the change from fine-grained calcareous sandstone of the member into mudstone of the Weald Clay Formation. Up-section change from thinly bedded, ripple marked, calcareous sandstone, locally lignitic (Horsham Stone Member, Weald Clay Formation) into silty clays, locally sandy immediately above the Horsham Stone Member (Weald Clay Formation).
Thickness: Between 1 and 2m generally, but up to 9m in the type area.
Geographical Limits: Central Weald, Surrey, Sussex. In a horseshoe-shaped outcrop centred around Horsham. The member can be traced as a prominent feature between Horsham and Crawley, but it also extends to the south and east of Christ's Hospital, Horsham, and extends as far as Cowfold, Bolney and Staplesfield (1:50K sheet 302). It also extends along the northern margin of the Brighton and Worthing district (1:50K sheet 318/333) from Twineham Green east to Wivelsfield and North Common. The member has been penetrated by a number of boreholes in the West Weald (Gallois and Worssam, 1993).
Parent Unit: Weald Clay Formation (WC)
Previous Name(s): Weald Clay Bed 1 (A&B). (-967)
Horsham Stone (-1604)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Reference Section  Woldringfold Park. Old sand pit shows 2.15m of strata in the lower seam of the member. Gallois and Worssam (1993, p.84). 
Reference Section  Warninglid No.1 Borehole TQ22NW/1 [TQ 2488 2701] between 48.16 and 59.21m depth. Lake and Thurrell (1974, 16-18). 
Reference Section  Southeast of Christ's Hospital. A temporary exposure of much of bed 1b. Gallois and Worssam (1993, p.81). 
Reference Section  A ditch section 1km east of Christ's Hospital. Bed 1b of the member seen including a 3m "khaki-brown" laminated siltstone. Gallois and Worssam (1993, p.81) 
Type Area  Haven Farm. Gallois and Worssam, 1993. 
Type Area  The member has a general outcrop south and west of Horsham particularly in the area around Christ's Hospital [TQ 148 285]; it continues south-eastward onto the Brighton Sheet area around Cowfold [TQ 214 227] and onwards towards the area [TQ 320 206] north of Burgess Hill. It outcrops again north-eastward from Horsham towards Crawley [TQ 275 360]. The original described sections are within numerous now defunct exposures described in Topley (1875, 102-104). A new exposure to recover heritage stone for renovation of buildings has been opened recently at Lower Broadbridge Farm, Broadbridge Heath [TQ 1421 3138] and this can now be considered the parastratotype for the member. 
Reference Section  The Gill, near Sedgewick Castle. "The upper division of the Horsham Stone is well exposed in stream sections" Gallois and Worssam (1993, 81-82). 
Reference Section  Long Wood. A stream section exposing Bed 1a. Gallois and Worssam (1993, p.82). 
Reference Section  Conies Farm. 1.2m of flaggy, buff, blue-hearted, calcareous sandstone of bed 1a. Gallois and Worssam (1993, p.84). 
Reference(s):
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. 
Worssam, B C. 1978. The stratigraphy of the Weald Clay. Report of the Institute of Geological Sciences, 78/11. 23pp. 
Mantell, G. 1827. Illustrations of the geology of Sussex. (London.) 
Topley, W. 1875. The geology of the Weald. Memoir of the Geological Survey of England and Wales. 
Lake, R D and Thurrell, R G. 1974. The sedimentary sequence of the Wealden Beds in boreholes near Cuckfield, Sussex. Report of the Institute of Geological Sciences, No.74/2. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E301 E302 E318