Royal Academy of Sciences of Paris. 147 



existence of the two species of fossils in the chalk formations disco- 

 vered by M. Dufresnoy in the south of France appears to break 

 down the distinct line of separation which exists between the ter- 

 rains tertiaires and the chalk in the north of Europe, we must have 

 recourse to the consideration of the relative number of the two 

 species of fossils, in order to see whether the anomaly and confu- 

 sion are so great as might be feared. The number of species of 

 shells and zoophytes which M. Dufresnoy has distinguished in these 

 strata is 124, of which 110 are determinable as genera. Of these 

 there appear to be only the following five which distinctly belong 

 to the terrains tertiaires, as well as to the chalk strata : Cardium 

 aviculare, Crassatella tumida, Cerithium diaboli, Nerita perversa, 

 and Tiirbinallia elliptica. There are about ten others, to which 

 M. Dufresnoy has not been able to assign names, but which he con- 

 siders to be identical with some of the species belonging to the ter- 

 rains tertiaires. Thus, at the outside, there are but 15 out of 124 

 which belong to the two species of deposits ; the 209 others have 

 always been recognised as belonging distinctly to chalk formations. 

 M. Brogniart then proceeds to establish, in an elaborate but lucid 

 line of argument, that a slight anomaly of this kind cannot diminish 

 the weight to be attached to zoological characteristics in determin- 

 ing the nature and epoch of a particular deposit. He remarks 

 that it is certain that every new deposit of earth must have been 

 occasioned by some extraordinary convulsion of nature ; and that 

 all experience shows us that the animals existing at one epoch dif- 

 fered so materially from those existing at another, as to enable us to 

 distinguish, by their organic remains, the relative epochs of the for- 

 mation of each deposit ; but it does not therefore follow that 

 in each of those convulsions of nature the whole of the then existing 

 species of animals were so completely annihilated as to prevent any 

 of them surviving or re-appearing in the succeeding epoch, in which 

 case the admixture of the different species of fossils will be accounted 

 for; only, as in this case, the number of those belonging to a pre- 

 ceding epoch will bear a very inconsiderable proportion to that of 

 those which properly characterise the epoch under examination. In 

 support of his opinion he cites the chalk formation discovered by 

 M. Merton in 1828, in New Jersey and Maryland, which contains 

 fossil remains similar, though not identical, to those of the chalk 

 of Europe, and also several of those which we have called litto- 

 ral, and attributed to the terrains tertiaires. Hence he concludes 

 that the zoological characteristics of strata form the surest guides 

 as to their nature and epoch, although their geognostic and mine- 

 ralogical characteristics may also be taken into consideration as 

 additional evidence. On these grounds, he considers that M. Du- 

 fresnoy has fully proved the existence of the chalk formations in the 

 south of France a discovery which is not only important as a 

 matter of information on the structure of that part of the globe, 

 but as affording a guide for useful mineralogical researches, founded 



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