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 : — 



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. 



