272 A. J. JUKES-BROWNE ON THE RELATIONS OE 



ation of the facts and statements given in the foregoing pages will, 1 

 think, inevitably lead to the following conclusions : — 



(1) That the Cambridge Greensand or nodule-bed has no connexion 

 whatever with the Upper Greensand or with the Warminster beds, 

 its actual position being above their horizon and at the base of the 

 true Chalk-marl. 



(2) That the same bed rests everywhere unconformably on the 

 clay below, and that the coprolites, fossils, and green grains which 

 it contains have been mainly derived from the denudation of the 

 Upper Gault, a formation which originally extended much further 

 in a north-east direction than it does now, but which is still well 

 developed in Buckinghamshire. 



(3) That in consequence of this erosion a great gap now exists 

 between the Lower Gault and the Chalk-marl in Cambridgeshire — 

 the whole of the Upper Gault, Upper Greensand, and Chloritic Marl 

 being absent, the first-named from denudation, the last two from 

 original non-deposition. 



There are still a few observations I wish to offer in support or 

 explanation of the conclusions arrived at above. 



(1) In following the Chalk-marl westward beyond the termination 

 of the Cambridge bed, we found it eventually underlain by the true 

 Upper Greensand in the shape of soft sands and calcareous sand- 

 stone, the former composing, at any rate in Berkshire, the chief and 

 most fossiliferous part of the formation. It thus continues, I be- 

 lieve, through Wiltshire into Devon ; in this county it has been 

 described by more than one observer, the last being Mr. C. J. A. 

 Meyer, who, in a paper read before the Society last session, gave a 

 careful description of the rocks of Beer Head and the adjacent cliff- 

 sections*. Among the beds there exhibited he identifies the Chlo- 

 ritic Marl in its usual position, and he maintains from a comparison 

 of faunas that the Warminster Greensand is also Chloritic Marl. If 

 this should prove to be correct, I think the Wantage sands will have 

 to occupy the same horizon, and the name Chloritic Marl would 

 simply indicate the topmost beds of the series hitherto called Upper 

 Greensand. According to Mr. Meyer the top of this Chloritic Marl 

 presents an uneven surface at its junction with the lowest bed of 

 the Chalk-marl, which, moreover, contains numerous phosphatic 

 nodules. Regarding the contents of this nodule-bed he observes 

 (p. 378) that " many of the fossils seem to have been deposited in 

 the condition of casts ; and some at least of these may have been 

 derived from a partial wearing away of the Chloritic Marl." Finally 

 he remarks " that this line of erosion is a fact of much importance 

 in its bearing on Cretaceous geology." 



In Devon, therefore, as in Cambridge, the Chalk-marl contains a 

 band of phosphate nodules at its base resting unconformably on the 

 beds below ; whether this line of erosion can be traced in the inter- 

 mediate country remains to be seen. I quite agree, however, with 

 Mr. Meyer in his estimation of the importance of these facts ; and 

 seeing how much more persistent and continuous the Chalk-marl is 

 * See Quart. Journ. Geol. Soc. vol. xxx. p. 369. 



