OF THE TTPPEE CRETACEOUS m WEST SUFFOLK AND NOKFOLK. 559 



hard, into which the dark-coloured gritty chalk above is let down by 

 pipes or mottlings for a foot or more ; becoming more yellow towards 

 the base, it passes into a grey-coloured marly clay, which contains 

 Belemnites. 



But the identification of this clay with the Gault, and the know- 

 ledge we have gained from the study of the beds at this horizon, both 

 in this neighbourhood and further to the north, shows that the true 

 stratigraphical position of the hard, grey, gritty chalk, with the 5 ft. 

 of lighter-coloured material beneath it, must be at the base and not 

 at the top of the Chalk- marl. 



We have here a section analogous to that seen immediately above 

 the Red Chalk in the cliffs at Hunstanton, viz. hard, creamy-white 

 limestone overlain by grey and gritty chalk with a layer of green- 

 coated nodules at its base, the so-called sponge- and Lioceramus-bedLS. 



Though between this hard chalk and the Gault the glauconitic 

 bed of Stoke Perry and Shouldham appears to be wanting, yet the 

 occurrence of Avicula grypliceoides at the base of the hard Chalk- 

 marl, both here and in the Grimston brook, is a palseontological 

 link which confirms our reading of the strata in this area. The 

 lower part of the hard Chalk-marl seen in the banks of the brook at 

 Grimston and at the Sow's Head spring has been described (see ante). 



We recognize the equivalent of the Totternhoe Stone in an old 

 pit three quarters of a mile N.E. of Sandringham Church. It is 

 here a bed of hard, grey, gritty stone, 2| feet thick, with a layer 

 of green-coated nodules at its base. Below it passes abruptly to 

 hard creamy-white material, which we refer to the Chalk-marl. It 

 is overlain by rather hard, dull, whitish chalk, the difference of colour 

 in the chalk above and below the stone showing it in some relief. 



A fine exposure of the lowest part of the Lower Chalk occurs in 

 the parish pit of Dersingham, and was described by Dr. Barrois in 

 1876. Dr. Barrois*, however, never assigned to the Totternhoe 

 Stone its true place in the series ; he at first supposed this stone to 

 be on the horizon which we now call the Melbourn Rock, and sub- 

 sequently he was led to regard it as belonging to the very lowest 

 part of the Chalk-marl f. Consequently, when he visited Norfolk 

 in 1875, he was quite unprepared to identify any representative of 

 the Totternhoe Stone which might there exist. No geologist, 

 however, excels Dr. Barrois in careful accuracy of observation, and 

 accordingly we find him recording a layer of hard, rolled, yellowish 

 or greenish nodules at a certain horizon both in the Dersingham 

 and Hunstanton sections. This layer of greenish phosphatic nodules 

 is identical with the " Brassil " of Cambridgeshire, and lies at the 

 base of the band of grey rock which we identify with the Totternhoe 

 Stone. At Dersingham it may be traced all round the pit, though 

 the nodules are more abundant and the layer thus more evident in 

 some places than in others. The band of compact grey chalk noticed 

 by Dr. Barrois as occurring above this is the Totternhoe Stone. 



* C. Barrois, " Recherches sur le Terrain Cretace Superieur de l'Angleterre 

 et de l'Irlande," p. 160 (Mem. Soc. Geol. du Nord). 

 t See Ann. Soc. Geol. du Nord, torn. iii. p. 145. 



2 P 2 



