Royal Academy of Sci ences of Paris. 143 



which was to prove that the marine deposits of the Mediterranean 

 basins of the departments of the Herault and the Aude corres- 

 pond, as to their position, with the coarse calcareous (calcaire 

 gros) formation of Paris, and not with the upper marine sands and 

 freestone. In this opinion, which is contrary to that of most geolo- 

 gists, M. Reboul stated that he had been confirmed by a comparison 

 of the fossils in the two basins. The lower marine deposit of the 

 south of France is, like that of the Sejne, covered with the gypseous 

 and siliceous calcaire of fresh water (eau douce), and in both basins an 

 upper, or rather mixed, marine deposit succeeds the fresh water 

 deposit. The essential difference between the lower deposits of the 

 south and those of the Seine is, that the former are free from all 

 mixture of fresh water fossils, and at the same time from concretions 

 of silex, of saline deposits, and even from compact, fine-grained 

 rocks. All these various productions are, on the contrary, found 

 in the upper or mixed earth of this basin, which forms a stra- 

 tum over the fresh-water deposits, or rather which is subordi- 

 nate to them. In the basin of Paris the same productions are found 

 in abundance in the upper stratum, but they are also found, though 

 in a smaller proportion, in the lower stratum. As the fresh water 

 deposits have, in this basin, preceded, or at least been associated, 

 with the first sediments of the calcaire gros, M. Reboul distin- 

 guishes basins of this kind by the name of prolymneens and by that 

 of metalynnieens those where the fresh water does not appear to 

 have penetrated until after the completion of the deposits of the first 

 epoch ; such are those of the Aude, the Oise, and the Herault. The 

 comparison of the sediments of these two species of basins opens a 

 new field of inquiry for geologists. 



On the Chalk Formations of the South of France. On the 25th of 

 April, M. Brogniart read to the Academy a most interesting report 

 on a memoir by M. Dufresnoy, entitled ' Des Caracteres particuliers 

 que presente le terrain de craie dans le Sud de France et sur les 

 pentes des Pyrenees. 3 The generality of the world, and even many 

 eminent geologists, have considered that they were fully acquainted 

 with the nature of chalk, from observing in the quarries its immense 

 masses without any distinct stratification, and its beds interrupted 

 by flint stones; but, having confined their attention to the external 

 and mineralogical characters of chalk, and neglected its geological 

 peculiarities, they have yet to learn that strata, which have not 

 the external character of white chalk with black silex, may and 

 do belong to the same period and the same geological formation, 

 because they possess the same peculiarities which, in the de- 

 posits of white chalk, form the true geological characteristics. 

 There are three modes of determining the rank which any deposit 

 occupies in the series of which the shell of the globe is composed. 

 1st. The nature of the strata which are constantly found above 

 or below it this is the geological characteristic ; 2dly, the nature 



