268 A. J. JUKES -BROWNE ON THE RELATIONS OF 



longer be there. These statements, moreover, cannot be applied to 

 the Upper Gault of Bucks, where Mr. Fisher will find the coprolites 

 to be of larger size, dark- coloured, and accumulated in a bed fully- 

 equalling the thickness and sandiness of the Cambridge stratum. 

 The nodules from the marly and clayey greensands above-mentioned 

 would necessarily be filled with a similar matrix. The Gault, 

 moreover, above these beds is so marly and light- coloured that it might 

 easily be mistaken for Chalk -marl on a first inspection. 



Resuming the track of the Gault nodule-bed, another pit is found 

 between Cheddington and Northall, showing a similar section, 

 namely : — 



4. Gravel and top earth. 



3. Light slate-coloured gault. 



2. Coprolite-bed with green grains. 



1. Dark blue gault. 



I obtained here the following fossils :- 



Ichthyosaurus (vertebrae). 

 Otodus appendiculatus, Ag. 

 Ammonites splendens, Sow. 

 cratus, Seeley. 



Plicatula pectinoides, Sow. 

 Spondylus gibbosus, If Orb. 

 Pleurotomaria, sp. 



These and the fossils in the preceding lists are all species common 

 in the Upper Gault of Folkestone and in the Cambridge Greensand. 



Mr. Wilkerson, of Leighton Buzzard, who manages the workings 

 at Cheddington and Northall, informs me that the thickness of the 

 Gault below the coprolite-bed is here about 150 feet, while to the 

 south, at Eddlesborough, it has a total thickness of 205 feet ; this, 

 therefore, leaves about 50 feet of Gault above the seam of coprolites, 

 which I propose to consider the line of separation between the Upper 

 and Lower Gault in this area. 



The line of workings which we have been following is continued 

 by another pit at jNorthall Common, and a fifth near Billington ; but 

 these I had not time to visit. Beyond this I am not aware of any 

 workings in the bed ; but Mr. Wilkerson told me that in the 

 second cutting in the railway, north of Harlington, the same band of 

 coprolites was met with, and light- coloured clay above them. 



Mr. Pearse, of Harlington, also told me that coprolites occurred 

 about 20 feet down in the clay -pit on the right-hand side of the 

 road to Toddington. 



Again, at Grange Mill, near Sharpenhoe, two layers of coprolites 

 were visible in a road-side cutting, surmounted by the usual light 

 marly clay of the Upper Gault. 



At the pits between Barton and Sharpenhoe the foreman told me 

 that he had bored for this lower seam on the other side of the road, 

 just outside the boundary of the Chalk-marl, and found it at a depth 

 of 18 feet. We may place its horizon here, therefore, at about 

 20 feet below the Cambridge bed, or 30 feet nearer the surface of 

 the Gault than it was ten miles further back to the S.W. This, then, 

 clearly shows either that the surface of the Gault is an inclined 

 plane, or that the nodule-bed below is inclined and rises upward 



