134 MESSES. A. J. JUKES-BROWNE A2Q) W. HILL: [May 1896,, 



3. The Cenomanian Sands of the Southern Orne and 

 Sarthe. 



We now come to a region which has been well explored by 

 Messrs. Paul Bizet and Albert Gnillier. The great change from a 

 chalky to an arenaceous facies begins to set in between Gace and 

 Mortagne, and, curiously enough, this occurs at the very top of tbe 

 formation, beds of sand coming in above the ' Craie a Ammonites 

 rotomagensis/ These are the ' Sables du Perche,' and it is interest- 

 ing to find that they contain fossils which we are accustomed to 

 associate with much older deposits (Chalk Marl and Upper Green- 

 sand). M. Bizet mentions, as common fossils, Ammonites navicu- 

 laris, Ostrea carinata, Bliynchonella compressa, with many shells- 

 of Exogyra conica and E. columba. 



Near Mortagne the sequence is given by M. Bizet 1 as follows: — 



4. Sables du Perche a Ammonites navicular is. 



3. Craie de Eouen a Ammonites rotomagensis. 



2. Craie glauconieuse a Ammonites Mantelli. 



1. Glauconie et argile glauconieuse a Ostrea vesiculosa. 



The Craie de Kouen is a thick mass of chalk which is divisible 

 into two parts or zones : (1) an upper zone of Scaphites cequalis, 

 which consists of alternating beds of firm chalk and greyish marl ;. 

 (2) a lower zone to which he does not assign any particular fossil, 

 but which consists of chalk with nodules of greyish flint. 



The Craie glauconieuse is evidently like that which we have 

 described at Yimoutiers and elsewhere, but M. Bizet seems to 

 include in it what we regard as the uppermost beds of the * glau- 

 conie ' or Greensand. Thus, in his excellent paper on the ' Profit 

 geologique du Chemin de fer de Mamers a Mortagne/ he writes : — 

 * Above the greensand come more or less argillaceous marls and 

 sands, then alternations of glauconitic sand and beds of a kind of 

 greenish or yellowish chalk, always containing many green grains." 

 He classes both these in the zone of Ammonites Mantelli, but we 

 did not find that fossil in the argillaceous marl, and, as already stated, 

 for us the base of the Cenomanien is at the top of this marl and 

 at the base of the yellowish chalk. 



Near Mortagne and Belleme the lowest Cretaceous deposit is the 

 ' Glauconie a 0. vesiculosa? This is a sandy marl or clay, which in 

 some places, and especially in the east of the department, contains 

 phosphatic nodules ; its thickness is only from 3 to 10 feet, and 

 Ostrea vesiculosa is the sole fossil found in it. At Ceton, however, 

 on the eastern border of the Orne, a representative of the Upper Gault 

 or Gaize comes in below this ' glauconie ' — a glauconitic clay with 

 phosphatic nodules and casts of fossils, among which are Ammonites 

 inflatus, A. auritus, and Area carinata. Ammonites splendens has 

 also been found in the same bed at Souance, near Nogent-le-Rotrou. 



It is clear, therefore, that the Upper Cretaceous sequence in the 

 east of the Orne is nearly as complete as in the Calvados, and that 

 it is merely a question as to where the line for the base of the 

 Cenomanien should be drawn. 



1 Bull. Soc. Geol. Normandie, vol. viii. (1881) p. 40, and vol. xi. (1885) p. 58. 



