THE CAMBRIDGE GAULT AND GREENSAND. 269 



towards the surface. Beyond this point I could find no sections or 

 exposures until I reached Shillington, four miles to the N.E. 



Here I made diligent inquiries about the Gault nodule-bed ; but 

 the foremen and well-sinkers knew nothing of any such seam, 

 though all agreed in asserting the existence of another bed of copro- 

 lites, about 180 feet down, near the bottom of the Gault, which has 

 here the usual thickness of 200 feet. 



This bottom bed I found was worked near Campton, about two 

 miles to the northward, and I subsequently visited the pit ; but the 

 seam of coprolites had of course no connexion with that I was 

 searching for. 



At Arlesey, a few miles to the east (see Map, p. 259 ) f there is a 

 large brickyard where excavations have been made to a depth of 

 50 or 60 feet in the Gault ; and if any nodule-band existed near the 

 surface, it would be discoverable in the steep sides of this pit. These 

 I carefully examined, but without finding any band or seam of co- 

 prolites ; nor did the men at work know of aDy such bed. 



I think, therefore, we are driven to one of two conclusions regard- 

 ing the Buckingham nodule-bed — either that it has thinned out 

 before reaching Shillington, or that it has cropped out into the 

 Cambridge bed somewhere between that place and Barton. In 

 order to decide this point completely, it would probably be necessary 

 to institute a series of borings over the district ; but I am strongly 

 inclined to believe that the latter supposition represents the true 

 state of the case. 



At the last place where I saw the bed (not five miles from 

 Shillington) it showed no signs of thinning out ; there is, moreover, 

 the remarkable coincidence that both the Cambridge and Buck- 

 ingham beds are last seen in the neighbourhood of Barton, and the 

 fact that they are there only 20 feet apart from one another. 

 Under the circumstances, therefore, I conclude that the stratum 

 which is worked for " coprolites " in Bucks has furnished some, at 

 least, of the fossils and nodules now composing what has been called 

 the Cambridge Upper Greensand. 



§ 5. The Gault and Greensand of the Weald. — I have now described 

 the relations of the strata in the districts which border upon the Cam- 

 bridge area; but before drawing my conclusions from the evidence 

 thus obtained, it will be desirable to take a short survey of the 

 deposits of a similar age in the Weald of Kent, which are capable 

 of throwing much light upon the question in hand. 



The following details are derived partly from my own notes made 

 at the commencement of this year, and partly from those of Mr. Price 

 and Mr. Topley, to whom my thanks are due for their ready kindness 

 in imparting such information as they possessed. 



Commencing, then, with the well-known section at Folkestone, the 

 thickness of the Gault here is given as 100 feet by Mr. Price, who 

 divides it into a lower and an upper division*. The main part of the 

 latter is formed by the bed numbered XI. in Mr. Price's paper, 

 which is 56 feet thick, and includes a band of fossiliferous and 

 * "On the Gault of Folkestone," Quart. Journ. Geol. Sois. vol. xxx. p. 342. 



