The distribution of the Kimeridge Clay in the neighbourhood of Cambridge is shewn on the Survey maps, sheets 51 N.W. and 51 S.W. I have not seen any exposures in it to the south or west of Knapwell. A narrow band of the clay runs from Knapwell, through Boxworth, Oakington and on to Cottenham; it then spreads out for some miles to the north and east, and underlies the large tract of fen-country of North Cambridgeshire. Near Ely the Kimeridge Clay is overlain unconformably by the Lower Greensand, and several outliers of these sands occur to the west and south-west of Ely, forming low hills in the fens.

The Kimeridge Clay is formed of dark and bluish-black clays, which are often laminated and occasionally quite bituminous. Sometimes these clays are very arenaceous, and contain small crystals of selenite. Several beds of grey-argillaceous limestone occur in the clay; they do not exceed a foot in thickness, and may be either in the form of regularly bedded limestones, or as layers of interrupted septarian nodules. The nodules are ellipsoidal in shape, and their longest diameter varies from one to three feet; they are composed of grey compact limestone; with their interior much fissured, and the fissures filled or lined with calcite. Fossils are fairly common throughout the clay, but they are not, in all cases, well preserved. Fragments of fossil wood are not unfrequently met with.

The sections in this clay are not very numerous: the following are the principal ones which I have observed.