102 MESSRS. A. J. JUKES-BROWNE AND W. HILL : [May 1 896, 



and (3) chalk, to which he gave the simple names of (1) The Gault, 

 (2) The Greensand, and (3) The Chalk. His Chalk was subsequently 

 divided first into Lower and Upper, and more recently into Lower, 

 Middle, and Upper. For a long time the Gault and Upper Green- 

 sand were regarded as distinct formations or stages, but the 

 tendency of modern opinion has been to consider them as different 

 lithological phases of one formation or stage, and we have no doubt 

 that a new name will have to be found for this combined Gault-and- 

 Greensand stage. 



The work of English geologists has therefore tended to consolidate 

 the Gault and Greensand, and to separate them as a whole from the 

 overlying Lower Chalk, which has generally a bed of glauconitic 

 marl at its base, and is often marked off from the Upper Greensand 

 by a very clear plane of division. The fossil assemblages agree 

 with this method of classification, and no modern English geologist 

 would imagine that a more natural division could be made by 

 grouping a part of the Upper Greensand with the Lower Chalk. 



This being so, it has for some time seemed odd to us that a 

 different line of division should be taken by French geologists, and 

 the question occurred to one of us whether they were fully justified 

 in correlating the beds which they group as Cenomanian. This idea 

 was greatly strengthened by a recent examination of the Devon 

 coast-sections where the Upper Greensand is well developed, but 

 the Lower Chalk is represented by a peculiar set of arenaceous beds 

 which differ from anything else in England. The fauna of these 

 beds is also peculiar. It includes Pecten asper, and many species which 

 in England are only found in the Upper Greensand*others which are 

 proper to the Lower Chalk, and some which have only hitherto 

 been found in France. Both of us were struck with the similarity 

 of this fauna to that of the French Cenomanian. 



Having thus obtained what promised to be a key to the difficulty — 

 for if Pecten asper occurred in a representative of the Lower Chalk 

 in England, it might do so also in France — we proceeded to enquire 

 how far this occurrence of P. asper might be responsible for the 

 supposed necessity of grouping the Greensand zone of P. asper in the 

 Cenomanian stage. We found that the succession of beds in the 

 department of the Sarthe had been carefully worked out, 1 that the 

 similar series in the Orne had been examined and described bv 

 M. Bizet, of Belleme, and that the Havre and Rouen sections had 

 been described by Prof. Hebert, M. Lennier, and others, but that 

 little or nothing was known about the intervening area in the 

 Calvados. So far as we could learn, no one had published any 

 detailed comparison of the succession in the Orne and Sarthe with 

 the sections near Havre, and consequently it was uncertain how far 

 south the Gault extended, and whether the base of the Cenomanian 

 in the Orne and Sarthe corresponded with any definite horizon at 

 Cape LaHeve. This want of continuous stratigraphical information 

 certainly seemed to leave much to be desired in the way of evidence, 



1 See G-uillier's ' Geolo°rie de la Sarthe.' 



