262 M. Desnoyers on the Chalk of the Cotentin. 



dier, Omalius d'Halloy, Constant Prevost, de Bonnard, and 

 Brongniart, have observed this hardening of the chalk in many 

 parts of Fi-ance, either in entire beds or in nodules. M. Elee 

 de Beaumont has observed many remarkable facts in the de- 

 partments of the Seine Inferieure, and Eure, at St. Etienne de 

 Rouvray, Louviers, Cauniont, Vernon, RoUeboise, in the pe- 

 ninsula formed by the Seine from Elbeuf to la Bouille : these 

 are, the occurrence, in the midst of loose beds, of unconnected 

 beds or masses, sufficiently compact, homogeneous, and sub- 

 lamellar to be worked as marble, the connection of which with 

 the upper chalk was observed by M. de Beaumont. Similar 

 deposits appeared to me to occupy the same situation at Cha- 

 teaudun (Eure et Loire). 



MM. Conybeare, Webster, Parkinson, Phillips, Mantell, 

 and Winch, have given numerous examples of this modifica- 

 tion of the chalk of the S.E. of England and Yorkshire, in their 

 memoirs. 



But to return to theValognes chalk : — No other bears so great 

 a resemblance to it in texture and composition as the spheru- 

 lite coarse chalk [crate grossierc a spherulites) of Sainonge, 

 Perigord, and Gascony. We have, in iact, the same union of a 

 compact and crystalline cement, penetrating a mass of the re- 

 mains of shells and corals ; the same alternation of friable and 

 solid, compact and granular beds ; in a word, it appears in 

 these cases to be the calcareous sand of Maestricht connected 

 by a spathose paste, the effect of a chemical solution postei'ior 

 to a mechanical deposit. 



Can these analogies, joined to the observed place of the 

 coarse chalk of Saintonge and Perigord, between the green- 

 sand [sable vert) and chalk with flints, suffice for supposing 

 the Valognes chalk to have occupied a precisely identical si- 

 tuation in the midst of the great chalk formation ? We have 

 seen that, in general, compactness is but a slight kind of ap- 

 proximation; and that from the assemblage of the other cha- 

 racters, the baculite limestone does not completely resemble 

 any one of the various divisions, elsewhere comprised between 

 ferruginous or iron sand [sable ferrugineux) and the tertiary 

 rocks. May we not presume that it is not identical with any 

 one of them, but thai, contemporaneous with them, it repre- 

 sents the whole in geological order, with variations produced 

 by the different circumstances of the deposits ? It will be ob- 

 served that these modifying circumstances must have been the 

 same in two other localities, above cited as approaching the 

 baculite limestone, Maiistricht and La Charente. Now, these 

 three chalk rocks arc remarkably analogous in being all de- 

 posited 



