| Lithological Description: |
| Limestone, off-white to pale brown fine- to medium-grained ooidal and coated peloidal grainstone, with common fine burrows, medium- to coarse-grained shell debris and flakes of greenish grey mudstone and dark lignite and minor amounts of fine-grained sand. Thick-bedded and cross-bedded or massive, weathering to flaggy or platy. Thin shell-detrital and ooidal marl and mudstone intercalations in places. Becoming very sandy eastward ("Swerford Beds" facies). Locally a mudstone bed ("Roundhill Clay" of Richardson, L, 1929) up to c.1m thick occurs at the base. |
| Definition of Lower Boundary: |
| Conformable/non-sequential on fine- to coarse-grained ooidal and peloidal limestone, locally ironshot, of Clypeus Grit Member. Oversteps northeastwards to rest non-conformably on Grantham Formation, Northampton Sand Formation and Whitby Mudstone Formation. |
| Definition of Upper Boundary: |
| Rapid passage upwards into mudstone-dominated Fuller's Earth Formation or Sharp's Hill Formation. |
| Thickness: |
| 0 to 12m |
| Geographical Limits: |
| North Gloucestershire to north Oxfordshire, where it passes northeastwards(on BGS 1:50 000 sheet 218) into the Horsehay Sand Formation (shown on 1968 edition of sheet 218 as the 'Lower Estuarine Series', now known as the Grantham Formation, but now thought to be generally absent south of Kettering). |
| Reference(s): |
| Cox, B M, and Sumbler, M G. 2002. British Middle Jurassic stratigraphy. Geological Conservation Review Series, Vol.26. (Peterborough: Joint Nature Conservation Committee.) |
| Richardson, L. 1929. The Country around Moreton in Marsh. Memoir of the Geological Survey of Great Britain. (Sheet 217, England and Wales). |
| Sellwood, B W and McKerrow, W S. 1974. Depositional environments in the lower part of the Great Oolite Group of Oxfordshire and north Gloucestershire. Proceedings of the Geologists' Association, Vol.85, 189-210. |
| Horton, A, Poole, E G, Williams, B J, Illing, V C and Hobson, G D. 1987. Geology of the country around Chipping Norton. Memoir of the British Geological Survey, Sheet 218 (England and Wales). |
