THE CAMBRIDGE GAULT AND GREENSAND. 265 



§ 4. Upper Gault in Bucks and Bedfordshire. — We have hitherto 

 followed the line of junction between the Gault and the overlying for- 

 mations. These in lineal succession were (1) the Cambridge coprolite- 

 bed, (2) the Chalk-marl without coprolites, (3) the Upper Greensand 

 in Bucks. This last, therefore, the true Upper Greensand, does not 

 pass into the Cambridge bed, but is separated from it by an interval 

 of about ten miles, in which bare Chalk -marl comes down on the 

 Gault. In this Chalk-marl and in the Upper Greensand the black 

 phosphate nodules, so abundant in the Cambridge bed, are entirely 

 wanting. 



Coprolites, however, are by no means absent in Buckinghamshire ; 

 but they are only obtained from a rich bed some 40 or 50 feet down 

 in the Gault ; we will now pass, therefore, to this lower horizon. 

 And just as we followed the Cambridge bed to the point where it 

 disappeared, so I think it will be most convenient to trace this Gault 

 nodule-bed back until it disappears and merges, as I believe, into 

 the Cambridge deposit of nodules. 



Starting, then, down the road which leads N.W. from Buckland, 

 and proceeding about a mile beyond the junction of Gault and 

 Greensand, a coprolite-pit is seen near the canal running between 

 Buckland and Puttenham ; and in it the following interesting section 

 was shown : — 



ft. in. 



3. Whitish marly clay, looking at a distance very like Chalk-marl, 

 but containing much " race " and a few light-coloured 

 phosphatic nodules 8 



2. Coprolite-bed, the upper part a grey sandy clay full of green 

 grains and coprolites, the lower part a stiff dark green sand 

 with rolled black nodules in abundance , 1 6 



1. Stiff, nearly black clay formed the bottom of the pit, appa- 

 rently unfossiliferous. 



Throwing the information obtained near Buckland and Aston 

 Clinton into the form of a diagrammatic section along a line from 

 the Chalk escarpment through the village of Buckland to this copro- 



Fig. 3. — Diagram Section from the Chalk escarpment through Buck- 

 land to the Aylesbury Canal. (Horizontal scale 2 inches to 1 

 mile.) 



Wendover Coprolite- Aylesbury 



Canal. Buckland. pit. Canal. 



a. Stiff dark Gault. g £ ^ f d. Flaggy calcareous sand- 

 X . Sandy marl, coprolite-bed. g^ g c \ stone with marly bands. 



b. White marly clay. t> o w 1 e ' Dark-green sands. 



c. Bluish sandy clay. /. Chalk-marl. 



