Geological Society of London. 137 



The first part of the paper deals with the stratigraphical relations 

 of the beds ; and the author calls attention to the fact that in the 

 numerous artificial sections near Cambridge only two formations are 

 really visible, viz. the Chalk Marl with a pebble-bed of phosphatic 

 nodules at the base, and the stiff dark clay of the Gault, upon which 

 these rest. 



The so-called Greensand or nodule-bed passes up into the Chalk 

 Marl, but rests unconformably on the Gault below, which presents in 

 fact a surface of erosion ; and there is therefore a break of indefinite 

 length between the Cambridge Gault and Greensand. 



The nodule-bed continues to present much the same characters 

 and fossils through Bedfordshire as far as Sharpenhoe, a village about 

 three miles east of Harlington, on the Midland Bailway. Here is 

 situated the most westerly coprolite pit or working in the Cambridge 

 bed ; and beyond this the Gault passes into Chalk Marl without any 

 such seam intervening. 



It is not until we enter Buckinghamshire and reach Buckland near 

 Tring, that anything like true Upper Greensand appears, and 

 separates the Chalk Marl from the Gault. From this point westward 

 the formation increases in thickness and importance, but its characters 

 and fossils are quite different from those of the Cambridge Greensand. 



Although in Bucks no coprolites are found between the Gault and 

 Greensand, yet they occur in the Gault itself; and one bed may be 

 traced towards the N.E., and is found to commence where the Cam- 

 bridge nodule-bed ends, thereby raising the presumption that it 

 becomes confluent with that bed, and has furnished many of the well- 

 known fossils and nodules it contains. 



A consideration of these facts warrants the following general con- 

 clusions : — 



I. That the Cambridge Greensand or nodule-bed has no connexion 

 with the Upper Greensand, its actual position being at the base 

 of the true Chalk Marl. 



II. That the same bed rests unconformably on the clay below, and 

 that its coprolites and fossils have been derived from the Gault. 



III. That in consequence of this erosion a great gap now exists in 

 Cambridgeshire between the Lower Gault and the Chalk Marl, 

 the whole of the Upper Gault and Upper Greensand being absent. 



The palaBontological evidence leads to exactly the same conclusions. 

 The fauna is divisible into two groups, and the fossils belonging to 

 the one are preserved in dark phosphate, and being generally water- 

 worn are clearly derived forms, while the others are of lighter colour, 

 and belong to the deposit. The former group is chiefly composed of 

 Gault species, seventy per cent, of which belong to the upper stage 

 of that formation; while the fossils proper to the deposit are also 

 found in the Chalk Marl above. 



The author therefore feels justified in concluding that strati- 

 graphically the bed is Chalk Marl, while palseontologically considered 

 its fauna is mainly derived from the Upper Gault. 



Discussion. — Mr. Charlesworth considered that the vexed question of the true re- 

 lations of the so-called Upper Greensand of Cambridge had been now determined, 

 and that it must be regarded as Gault. The presence of Endogenites erosa and other 

 Wealden forms in the deposit at Potton in Bedfordshire, would seem to show that 



