26 The Geology of Cambridgeshire 



highest beds of the local Gault are remarkably devoid of 

 determinate fossils. Hence, and on theoretical grounds, it has 

 been generally supposed that the Upper Gault proper was in 

 Cambridge entirely denuded soon after its deposition. 



A recent examination of the large pit, east of the New- 

 market Road at Barnwell, has proved the existence of a 

 richly fossiliferous horizon, some forty feet below the Cam- 

 bridge Greensand, and from this any quantity of Ammonite 

 varicosus may be collected. The fossil belt exposed is about 

 seven feet thick and has not yet been pierced ; it contains 

 occasional brown contemporaneous phosphate nodules through- 

 out. One of the beds is in places so rich in phosphate nodules 

 and shell fragments that it has to be rejected by the brick- 

 makers as * blowing ' the bricks, and it is exceedingly hard 

 and tough. The phosphate nodules occur in various states, 

 some being hard and compact while others are merely lumps 

 of partly phosphatized mud. All are unworn and are ap- 

 parently contemporaneous with the rest of the deposit. Grains 

 of glauconite are abundant, and these, with the shell fragments, 

 give the rocks the characteristic feel of certain beds of the 

 Upper Greensand of the south. The commonest fossils of the 

 band are ammonites, and examples of A. varicosus may be 

 observed up to a foot in diameter, and A. splendens is also 

 fairly abundant. A large concentrically striated Inoceramus 

 often three or four inches across is very plentiful and provides 

 most of the calcareous material for the hard bed. Other 

 interesting forms as Terebratula biplicata, Terebratulina 

 triangularis, Pecten orbicularis and Nucula bivirgata are 

 common. The whole fauna presents an aspect very similar to 

 that of the Upper Gault nodules of the Cambridge Greensand. 

 From this new evidence, therefore, we conclude that 'Upper 

 Gault' is not entirely absent in the neighbourhood of Cam- 

 bridge, but that at least forty of the one hundred and fifty feet 

 proved in well-sections at Barnwell must be ascribed to the 

 Upper Gault. 



The section at Barrington adds confirmatory evidence in the 



