164 F. L. Kitchin & J. Fringle—-The Upper Gault in 



Inoceramus sulcatus, which at Folkestone occur in Bed IX. 

 Inocerawus anglicus Woods has been obtained at Haldon. 



The silty and sandy beds constituting the lowest part of these 

 westerly developments of the English Gault were probably 

 accumulated with much greater rapidity than the more fossiliferous 

 basal part of the Upper Ga,ult clay in regions of deeper-water 

 sedimentation. It is evident that the conditions under which they 

 were laid down were unfavourable for cephalopod-life ; and the 

 general scarcity of fossils in the lowest beds may perhaps be taken to 

 show that the extension of the sea-floor proceeded so rapidly that 

 some time elapsed before faunal adjustments to the new conditions 

 could be brought about. We have noticed elsewhere that when the 

 character of the lowest beds of the transgressive Upper Gault is such 

 as to point to their deposition in water rendered turbid by currents, 

 fossils are scarce. 



Oxfordshire, Buckinghamshire, and Bedfordshire. — We have not 

 yet been able to visit sections showing the transgression of the Gault 

 on to the Jurassic rocks which occurs in places in Wiltshire and 

 Berkshire, and at Culham, in Oxfordshire. In Oxfordshire and 

 Buckinghamshire an area of deeper water deposition is reached, 

 where the formation attains a great thickness and the upper sub- 

 division is largely developed in clayey facies. In this region the 

 existence of an overlap of the Upper Gault is readily discernible. 

 A nodule-bed which, at some localities in these counties and in 

 Bedfordshire, occupies a position about 10 to 20 feet above the 

 base of the Gault was formerly worked for " coprolites ". The 

 fossils obtained included typical species of the Upper Gaalt (Bed IX 

 of Folkestone), showing clearly that the transgressive base of 

 the Upper Gault occurred at those places at least as low in the series 

 as at that level, if, indeed, Lower Gault was always present beneath." 

 Failure to recognize the discordant relation of the Upper to the Lower 

 Gault in this area gave rise to the appearance of an anomaly in the 

 distribution of some of the fossils known elsewhere to be confined 

 to the Upper Gault ; they were here supposed to occur in the Lower 

 Gault 1 because of their proximity to the base of the clay. The Lower 

 Gault through a considerable part of this district is overstepped by 

 the Upper Gault, which extends forward upon Wealden, Purbeck, 

 Portland, or Kimmeridge beds, as the case may be. 



An opening made by the Geological Survey in 1920 in a disused 

 pit at Long Crendon, near Thame, on the margin of an outlier of 

 Gault, showed 9 feet of Upper Gault with a well-defined basement- 

 bed, 1 ft. 6 in. thick, of ochreous sandy clay with ironstone and other 

 pebbles.2 -jj^jg rested upon a 2 ft. clay-band (Purbeck ?), underlain 

 in turn by a Purbeck limestone. In the Gault Clay immediately 



^ A. J. Jukes-Browne, The Cretaceous Bocks of Britain, vol. i, "The 

 Gault and Upper Greensand of England" : Mem. Geol. Surv., 1900, pp. 275 

 et seq. 



2 " Summary of Progress for 1920 " : Mem. Geol. Surv., 1921, p. 62. 



