Ihe Calcaire Grassier of Pans. 3 



estimation, one of the most remarkable facts that our researches 

 have brought to light. 



The mode we have employed to recognize a bed already 

 observed in one distiict, is the nature of the fossils contained 

 in each bed : these fossils are always of the same general cha- 

 racter in corresponding beds, and present very observable dif- 

 ferences in species from one system of beds to another. This 

 mode of recognition has not as yet deceived us. 



It must not however be supposed that the difference be- 

 tween one bed and another is as marked as that between the 

 chalk and calcaire grossier. If it were so, we should have so 

 many distinct formations; but the characteristic fossils of one 

 bed become less numerous in the bed above it, and either dis- 

 appear in those above the latter, or are gradually replaced by 

 others which had not before appeared. 



We now proceed to describe the principal systems of beds 

 observable in the calcaire grossier. The first and most in- 

 ferior beds are the best characterized ; they are very sandv, 

 often more sandy than calcareous. When they are solid, they 

 decompose in the air and fall into powder: the stone also 

 which they furnish is only capable of being employed under 

 particular circumstances. 



The shelly limestone of which they are composed, and even 

 the sand which sometimes replaces it, almost always contains 

 green earth, either in grains or powder. This earth appears, 

 from the experiments we have made, analogous in its compo- 

 sition to the chlorite baldogee, or Verona-earth, and to owe its 

 colour to iron. 



The following is an analysis that M. Berthier has made of 

 the Verona-earth and of the green grains found in the lowest 

 beds of the calcaire crossier. 



Silica . . 

 Protoxide 

 Alumina 

 Lime . . 

 Magnesia 

 Potash . 

 Water . 



of Iron 



Verona 

 Earth. 



0-68 

 0-17 

 0-01 

 0-00 

 0-07 

 0-00 

 0-06 



Green grains of 

 the limestone 

 beneath Paris. 



0-46 



0-22 



0-07 



0-03 



0-06 



0-00 



0-15 



Green grains of the 

 limestone in tiic 

 environs of Paris. 

 0-40 

 0-25 

 0-02 

 0-03 

 0-16 

 0-02 

 0-12 



, 0-99 0-99 1-00 



It will be seen that this earth is in general a silicate of iron ; 

 and it is probable, if it could be obtained more pure, that the 

 analogy between it and the Verona-earlh would be linuid more 

 complete. 



B 2 This 



