AND THE PHOSPHATIC BEDS NEAR MONS. 333 



The Tufaceous Chalk (C) passes transgressively over the Chalk of 

 Nouvelles(F), which directly underlies the brown phosphatic chalk d\ 

 A conglomerate (Foudinc/ue de la Mcdogne) app(?ars under the 

 Tufaceous Chalk, but another analogous deposit, to which M. Briarfc 

 and I have given the name of Conglomerate of Cucsmcs, is seen on 

 the denuded surface of the Chalk of iSouvelles. This conglomerate, 

 of which the thickness varies from a few inches to several feet, is 

 composed of brown nodules, so rich in phosphate of lime that it 

 sometimes exceeds 45 per cent. A great number of these nodules 

 are the interior casts of fossil shells. 



The above description will suffice to give a correct idea of the 

 extent and importance of the beds of phosphatic chalk in the 

 neighbourhood of Mous. To enable the reader to appi-eciate their 

 importance from their superficial area, the map (tig. 4) is here 

 given. It is a geological map, drawn to the scale of 1 : 100,000, 

 and in which the Tertiary deposits are not represented. The phos- 

 phatic beds are spread out in an elliptical basin, the greater axis of 

 which is in a direction from south-west to north-east and measures 

 5 English miles. The length of its smaller axis probably exceeds 

 3 miles ; nothing can, however, be affirmed with certainty on this 

 point, as the northern limit of the phosphatic deposit is not yet well 

 known. But its southern boundary has been traced as clearly as 

 possible, as laid down on the map ; it measures 8 miles in length. 

 It is along this southern limit that the phosphate workings are now 

 carried on. 



Up to the present time, the workings at Cuesmes, Ciply, and 

 Hesvin have only been carried to the surface of the underground 

 water-level, \\hich is found everywhere at a certain depth in the 

 Cretaceous strata in the neighbourhood of Mens. The Brown Phos- 

 phatic Chalk has there the greyish-brown tint of which I have 

 already spoken ; but towards the eastern extremity of the phosphatic 

 basin, between St. Symphorien and Havre, the workings are carried 

 on below the underground water-level. The Brown Phosphatic 

 Chalk there exhibits a colour strikingly different from that of 

 Cuesmes, Ciply, and ^lesvin. It is of a very dark bluish green, and 

 might from its appearance at first sight be confounded with certain 

 glauconiferous chalks occurring in several geological stages of the 

 neighbourhood of Mens. Nevertheless, as regards its chemical 

 composition, the phosphatic chalk of St. Symphorien and Havre 

 does not differ materially from that which is worked more to the 

 westward. The difference of colour seems to be due to different 

 degrees of oxidization of the small quantity of iron contained in the 

 rock. 



The oldest workings of phosphate of lime in the neighbourhood of 

 Hons were begun in 1872 ; but, having only for their object the 

 extraction and treatment of the nodules of the conglomerate of 

 Malogne, they were soon abandoned. 



