4; MM. Cuvier and Brongniart on 



This green, earthy, and granular silicate of iron is only 

 found in the lower beds: it is not seen either in the upper or 

 white chalk, in the (plastic) clay, or in the middle or upper 

 beds of the calcaire grossier, and its presence may be regarded 

 as a sure sign of the vicinity of the plastic clay, and conse- 

 quently of the chalk. The prodigious quantity of fossil shells, 

 is, however, the principal charactei-istic of this system of beds ; 

 the greater part of these shells are more unlike existing species 

 than those contained in the upper beds. 



Nummulites are found in this system of beds. They occur 

 either alone or mixed with madrepores and a few shells. We 

 have found them near Villers-Cotterets, in the valley of Vau- 

 cienne, at Chantilly, and at the descent of Morlaye. They 

 are mixed with well-preserved shells, and with large grains 

 of quartz which form this rock into a kind of conglomerate; 

 as at Mont Ganelon near Compiegne, Mont Ouin near Gi- 

 sors, &c. 



Another characteristic of the shells contained in this system 

 of beds, is, that the greater part are entire and well preserved, 

 that they are easily separated from the rock, and that many 

 of them have still preserved their nacre. 



The other systems of beds are less distinct. The middle 

 beds still contain an abundance of shells. We should notice 

 a bed, sometimes soft and often possessing a green tint, whence 

 the name banc vert given it by the workmen, and sometimes 

 hard and of a yellowish gray colour. Brown impressions of 

 leaves and stems of vegetables are frequently found in the 

 lower part of this bed mixed widi Cerithia, thick Ampullaria, 

 and other marine shells. The greater part of these vegetables, 

 which are very delicate and varied, cannot be referred to any 

 marine plant; the bed containing them is seen at Chatillon, 

 St. Nom, Saillancourt, &c. that is to say, over an extent of 

 nearly ten leagues. 



The third or upper system contains fewer shells than the 

 two preceding. In this we can often recognize, 1. Yellowish 

 or gray beds, sometimes soft, at others very hard and con- 

 taining Lucintv, Amjndlaricc, and Cerithia, which sometimes 

 occur in vast (juanticies. The upper and middle of this part is 

 often very hard, affortls an excellent building-stone, and is 

 known by the name of ;oc7/c. 2. Near the top, a bed of little 

 thickness, but hard, and remarkable for the prodigious quan- 

 tity ol" small elongated and striated Corbulcc, found in the hori- 

 zontal fissures. These Corbulas occur in an horizontal posi- 

 lioti, pressed closely against each other. They are generally 

 white. 



Above the last beds of the calcaire grossier, the hard cal- 

 careous 



