Handbook to the natural history of Cambridgeshire / edited by J.E. Marr and A.E. Shipley.

Date:
1904
Catalogue details

Licence: In copyright

Credit: Handbook to the natural history of Cambridgeshire / edited by J.E. Marr and A.E. Shipley. Source: Wellcome Collection.

    30/310 (page 18)
    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 Greensand, 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 unconform ably 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 hed 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