Vol. 52.] A DELIMITATION OF THE CENOMANIAN. 175 



prolonged study of the Cretaceous rocks of England he would have 

 arrived at the same conclusion as we have. 



It is indeed much to be regretted that Dr. Barrois did not carry 

 out his intention of visiting Normandy, for there is no other 

 Frenchman who has so extensive a knowledge of the Upper Creta- 

 ceous series in England and Prance. It would appear that the 

 French have not yet indicated the place of the Craie de Rouen in 

 the coast-section ; that is to say, they have not divided this section 

 into a zone of Ammonites rotomagensis and a zone of A. Mantelli, 

 as at Vimoutiers. As regards its correlation with English sections, 

 the French view rests apparently on three points of similarity 

 between their ' Craie glauconieuse ' and our Upper Greensand, such 

 as would naturally strike any one who knew the English Chalk and 

 Greensand only from published descriptions ; these are : — 



(1) The large amount of glauconite in the Cenomanien. 



(2) The occurrence of frequent layers of chert. 



(3) The presence of Pecten asper and other fossils common in the 



4 Warminster Greensand.' 



"We will take these points seriatim. (1) It is a mistake to 

 suppose that the material of the ' Craie glauconieuse ' resembles that 

 of our Greensand. The very use of the word ' Craie ' indicates the 

 difference, and is quite correct in the department of Seine Inferieure, 

 where the matrix does consist of fine chalky matter. Our Upper 

 Greensand, on the contrary, is a sand consisting of quartz and 

 glauconite, though it is sometimes cemented by calcite into a calca- 

 reous sandstone. 



(2) The occurrence of layers and lumps of true chert does un- 

 doubtedly create a superficial resemblance between the two sets of 

 strata ; but the researches of Dr. Hinde have so completely proved 

 the connexion between the formation of cherts and the existence of 

 siliceous sponges, that the mere occurrence of cherts can only be 

 taken as evidence of the conditions being locally favourable to the 

 growth of such sponges. 



(3) The presence of Pecten asper and other fossils, which in 

 England are chiefly found in the Upper Greensand, is the sole argu- 

 ment that requires serious consideration. Let us first of all see 

 what it amounts to when admitted without any qualification. 

 Where does this special fauna exist in England ? Certainly not in 

 the Chert Beds either of Wiltshire, Dorset, or the Isle of Wight, 

 which have everywhere a very limited fauna. What are usually 

 called l the fossils of the Warminster Greensand ' have mostly been 

 obtained from a bed of bright green sand (about 10 feet thick) 

 lying above the Chert Beds, and passing up into Chloritic Marl with 

 phosphate-nodules and Stauronema Carteri. It is only here, just 

 below the base of the Chalk, that the Chalk Marl cephalopoda make 

 their first appearance in England, and are associated with Ptden 

 asper and other fossils which very shortly disappeared from the 

 English part of the Cretaceous sea. It is quite a mistake to suppose 

 that this is a typical Upper Greensand fauna ; it is only that of the 



