COKNET AND BRIART CALCAIRE GROSSIER OF MONS. 13 



2nd. Grey sand, slightly glauconitic, coloured yellow in some 

 places. It is impossible to draw a sharp line of demarcation between 

 this and the lower bed, the passage of the one into the other being 

 characterized by an insensible diminution of the giauconite and the 

 white matrix, leaving nothing but a mixture of grains of quartz 

 with a few of giauconite, which gives to the rock a greenish-grey 

 appearance. 



3rd. Blue ferruginous clay, variegated with yellow. 



4th. Very ferruginous yellow sand. 



A section between Mons and Ath, obtained some years ago by 

 M. Lebreton-Dulier while sinking a shaft in a search for coal, is 

 described as affording evidence of the greatest importance. After 

 passing through 3^^ feet of black sand (surface- soil), and 26 feet of 

 grey sand containing some grains of giauconite, 20 feet of very green 

 sand was reached, repos^'ng upon the debris of rocks, of which rehable 

 specimens were not obtained. 



This green sand is in its mineralogical character identical with 

 that overlying the " calcaire grossier" of M. Goffint's well (no. 5 of 

 section, p. 11) ; it rested upon a soft greyish-yellow limestone, con- 

 taining at different depths thin beds of hard white limestone. This 

 limestone was 305 feet thick, and contained fossils of which eight 

 species have been identified with those obtained from the weU of 

 M. Goffint ; they belong to the genera Nematura, Melanopsis, and 

 Cerithium. 



The absence of Pholadomya KonincJdi from the glauconitic sand 

 to the north-east of Mons is ascribed by the authors to the softness 

 of the " white matrix" (see p. 12) in that district. This softness 

 decreases towards the south-west ; and near Angres and Tournay, 

 in that direction, Pholadomya KonincTcii is abundant. 



The authors then trace tlie several beds which they have described 

 from the cemetery at Mons to about fojty-four yards to the north of 

 the road to Charleroi, where they underlie the beds characteristic of 

 the " Paniselien" system of M. Dumont, which are there seen in situ. 

 Upon this they remark that " the glauconitic bed of our sections, and, 

 with greater reason, the limestone with the Tertiary fauna, which it 

 overlies to the north-west of Mons, are inferior to the ' Paniselien' 

 system and to the sandy and argillaceous beds which form the base 

 of it — beds which we refer, according to the geological map of 

 M. Dumont, to the ' Landenien' and ' Ypresien' systems." 



The " calcaire grossier" of the well of M. Goffint seems to occupy 

 a vast depression or hollow in the chalk, and to correspond in its 

 palseontological character to some parts of the upper sands of Sois- 

 sonnais (sables superieiirs du Soissonnais) and the " Calcaire gros- 

 sier " of the Paris basin. 



In conclusion, the authors point out other localities, in the neigh- 

 bourhood of Mons, where the same disposition of beds is known to 

 occur. 



In reference to this subject M. d'Omalius d'Halloy, who, in con- 

 junction with M. Dewalque, reported on MM. Cornet and Briart's 



VOL. XXII. PART II. E 



