18 The Geology of Cambridgeshire 



between the pits. Such undulation can also be abundantly 

 proved by a consideration of the well sections at some of the 

 farms. 



Limestone beds like those about Upware extend all along 

 the ridge nearly to Barway a total distance of about three 

 miles. The width of the ridge is about one mile, and a well 

 boring near Wicken has proved the absence of limestone 

 there. 



Kimeridgian. 



Overlying the Ampthill Clay in all places where that 

 formation is present in its entirety is the Kimeridge Clay. 

 South of Knapwell the whole of it had been removed before 

 the deposition of the Lower Green sand, but further north 

 the diminution of the unconformity allows the coming in 

 of higher and higher beds, and a consequent widening of the 

 outcrop. 



The Kimeridge Clay appears to lie conformably on the 

 Ampthill Clay, and a line of phosphatic nodules is taken as 

 the horizon at which to separate the two. At Upware, at the 

 north-east end of the inlier, Prof. W. Keeping found that the 

 Kimeridge Clay lay unconformably against a bank of Coral- 

 lian limestone, but no exposure of such a section has since 

 been seen. 



The phosphate nodule bed has been observed in the now 

 overgrown pit at Knapwell, and in a pond and ditch west of 

 Oakington, also near Willingham, Haddenham Fen, and in the 

 brickyard half a mile west of Haddenham station, which is 

 still worked down to the bed in question. It is also known 

 in the Chettering boring. The clay immediately above the 

 nodules at Haddenham is very dark in colour and has an 

 extraordinary abundance of Ostrea deltoidea, both large and 

 small. 



The Kimeridge Clay, like the underlying Ampthill and 

 Oxford Clays, is variable in character ; it is in general darker 

 and more finely laminated than either. In its upper portions 



