Miscellanies. 197 
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. 
With 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. : ore i 
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. 
© same thing holds good in sixteen species of the second epoch ; 
the greater number of which are found in Senegal, Madagascar and 
