GEOLOGY 



but it is not known what older formation occurs below. Paljeozoic 

 rocks, possibly even Coal Measures, might be found, as may be inferred 

 from the fact that at Harwich old slaty rocks, presumably Silurian, were 

 reached at a depth of little over i,ooo feet ; and at Stutton, in Suffolk, 

 similar rocks were found at a little less than i,ooo feet — in both cases 

 immediately below the Gault. 



In a well-boring at Holkham, clay, presumed to be Kimeridge 

 Clay, was touched at a depth of 743 feet from the surface beneath the 

 Lower Greensand ; but the evidence was not satisfactory, as the clay may 

 belong to the Lower Greensand. We know nothing eastwards of this 

 locality of any beds beneath the Gault in Norfolk. 



Hence in any trial-borings for Coal Measures it would be necessary 

 to estimate in the western part of the county for a considerable thickness 

 of Jurassic clay beneath a reduced thickness of the Chalk, etc. ; while in 

 eastern Norfolk, although there would be a much greater thickness of 

 Chalk, yet the Palaeozoic floor might be reached immediately beneath 

 the Gault.* 



OXFORD AND CORALLIAN CLAYS 



The oldest formation which has been proved in Norfolk is the 

 Oxford Clay, a marine mud well developed in the neighbourhood of 

 Oxford, and which forms vales of meadow land across the country from 

 Dorset to Lincolnshire. A boring made in 1827 at Lynn to a depth of 

 630 feet, was carried through about 50 feet of alluvium and 580 feet of 

 Jurassic clays. These clays include portions of the Oxford Clay with 

 Gryphaa dilatata ; of overlying Corallian Clay with Ammonites decipiens^ 

 Bekmnites abbreviatus, and Ostrea bullata ; and of Kimeridge Clay with 

 Ostrea deltoidea. 



Corallian clay may also occur beneath the alluvium at Denver 

 Sluice, south-west of Downham Market, where Ammonites decipiens has 

 been obtained.* 



KIMERIDGE CLAY 



The oldest formation which comes to the surface in Norfolk is the 

 Kimeridge Clay, so named from its development at Kimeridge, on the 

 Dorset coast. 



It consists of dark blue, almost black, clay and shale, with 

 occasional cement-stones, or septaria, and bands of limestone ; and it has 

 been dug for the manufacture of bricks and tiles at Downham Market, 

 Watlington, and West Winch. As a formation it enters very little into 

 the structure of the county ; it forms part of the islet in the Fens on 

 which Southery is situated, and it borders the eastern side of the Fenland 

 from Downham Market to a little north of Lynn, concealed in places by 

 intervening portions of marshland. Its soil, naturally a stiff clay suitable 



* See H. B. Woodward, * Geology of Norwich' {Geol. Survey), 1881, pp. 6, 169. 



* See H. B. Woodward, 'Jurassic Rocks of Britain' {Geol. Survey), vol. v., 1895, pp. 61, 147. 

 (References are there given to observations by C. B. Rose and Fitton.) 



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