GEOLOGY which phosphatic nodules and a few fossils such as Belemnites attenuatus, fish-vertebra^, etc., have been observed/ Its thickness may be greater under Mildenhall Fen, probably as much as 90 feet. At Stutton the Gault was reached at a depth of 944 feet, and its thickness was about 50 feet. It there rests directly on Palccozoic rock. No evidence of Upper Greensand has been met with, for although at Combs near Stowmarket the lower part of the Chalk was proved at a depth of 874 feet, and green sandy beds and clays were then reached, these may in part belong to the base of the Chalk, as noted further on." CHALK While the Chalk enters so much into the foundation of the county, it is only in the western parts that it appears to any prominent extent at the surface. Elsewhere it is largely concealed by newer deposits, and on the eastern side it lies more than 200 feet below the surface of Orford marshes, 126 feet at Saxmundham, and as much as 475 feet at Lowes- toft. The full thickness proved in the deep boring at Stutton amounts to 874I feet, a good deal less than that known to occur in Norfolk. In other localities thicknesses of over 800 feet have been proved, as at Landguard Fort (base not reached), and at Combs near Stowmarket, where the highest beds of Chalk were not present. The divisions recognized in the Chalk are as follows : — Zones Upper Chalk Chalk with flints: Chalk Rock at base Actinocamax quadratui Manupites Micraster Holaster planus Middle Chalk Bedded Chalk with few flints : Melbourn Rock at base TerehratuUna Rhynchonella cuvieri Lower Chalk Grey Chalk or clunch : Tottern- hoe stone at base Chalk marl Holaster subglobosus Ammonites varians In the eastern part of the county it is probable that the lowest portion of the Chalk formation is a dark green glauconitic marl a few feet thick, recognized in some deep borings, as at Stutton, and belonging perhaps to the sub-zone of Stauronema carteri.^ In the western part of the county it is likely that the Cambridge phosphate bed may occur at the base of the Chalk, as it was proved in a boring at Isleham, and it has been worked near Soham in Cambridgeshire. In this case it would
- Whitaker and Jukes-Browne, ^art. Journ. Geol. Soc. 1. 49 1 •
2 Whitaker, Geol. Mag. (1895), p. 465; Jukes-Browne, 'Cretaceous Rocks of Britain,' vol. i. (1900), Geol. Survey, pp. 372, 373. ' Jukes-Browne, ' Cretaceous Rocks of Britain ' vol. i. (1900), Geol. Survey, p. 373.
