Miscellanies. 1D7 



pond, with the two series already determined, although with less pre- 

 cision, by their mineralogical relations. The first, which is the most 

 considerable and the most ancient, and which is known under the 

 name of secondary formation, contains not a single fossil species, 

 which has an analogous fossil in the second series ; so that every 

 race of this epoch is not only now extinct, but most have been so 

 when the formation of the second series began. This assertion does 

 not seem to accord with some of the results announced by M. Du- 

 fresnoy ; but this was not the principal object of the memoir ; and 

 M. Deshayes directs his attention almost exclusively to the second 

 series, which comprehends the tertiary formations properly so called. 

 Widi this series, says the author, begins a new Zoology, which, in 

 its ensemble has intimate relations to that which actually exists, and 

 is connected with the present epoch, because it shows us, in propor- 

 tions varying in each stratum, fossil species identically the same as 

 those which now exist. 



In tertiary formations, M. Deshayes discovers three distinct 

 groups, corresponding to three different periods of formation. 



In the first group, which is the oldest, the number of species thus 

 far determined is about three hundred, of which forty two are found 

 in a fossil state in the following groups, and thirty eight are analo- 

 gous to living species. 



In the second, there are more than nine hundred species, of which 

 seventy three are found in the superior formation, and one hundred 

 and sixty one are analogous to living species. 



For the third epoch, the proportion between the number of species 

 still living, and those which are lost, is much increased. It is in the 

 first group, three per cent. ; in the second, nineteen per cent. ; in 

 the last, more than fifty per cent. ; that is, of seven hundred fossil 

 species belonging to this group, about three hundred and sixty have 

 their analogies among the shells which people our waters. This 

 third epoch forms, of course, in some sort, the commencement of the 

 actual state of things. 



Another enquiry still remained, namely, to compare the-actual dis- 

 tribution of shells which have their analogous fossils with the ancient 

 distribution over the globe. The author has ascertained that of the 

 thirty eight living species of the'first group, some are found in almost 

 all latitudes, the greater number, however, in the intertropical regions. 

 The same thing holds good in sixteen species of the second epoch ; 

 the greater number of which are found in Senegal, Madagascar and 



