M. De CandcUe on Fossil Vegetables. 95 



the epoch of the coal-measures, the diversity in contemporaneous 

 regions has become more evident. 



V. On the Connection between the Vegetables of the 

 SEVERAL Epochs and the successive Periods, 



An important fact pervades the history of fossil vegetables ; 

 it is this, That the same species has been rarely to a certainty 

 Jbund in two different formations, and never in two formations 

 which are separated by tzao or more formations. 



It would appear that the revolutions of the globe, which at 

 different epochs have suddenly produced a change in the nature 

 of the soil, have destroyed all, or nearly all, the kinds of vege- 

 tables which were then flourishing; and that after every com- 

 motion of this sort, new varieties have appeared above the older 

 strata. Throughout the whole thickness of the same bed, little 

 variety of the same kinds are found ; and nothing indicates that 

 there have been gradual modifications of forms, by which the 

 species would have passed insensibly from the one formation or 

 epoch to another. 



Between the vegetable species of two successive formations, it 

 often indeed does happen that there are sufficiently striking 

 alliances. They usually belong to very nearly the same genera, 

 or to the same families ; and the proportion of the species of 

 each great class differs but little. Sometimes the same species 

 has been found in two superimposed and analogous formations. 

 But this is a coincidence of very rare occurrence. The pro- 

 dromus of M. Brongniart contains three species common to 

 the formations of the transition and coal series, four common to 

 the lias and the Jura formations, and one to the Jura, and the 

 chalk formation. 



Occasionally we find a formation covered by a stratum of a 

 totally different nature, which usually contains a very few orga- 

 nized beings which have lived in salt water ; then above this 

 stratum other and very different formations commence, in which 

 the proportions of the great classes of vegetables is no longer 

 the same, and where the species never resemble those which 

 have preceded. M. Brongniart has availed himself of these re- 

 markable facts to group tiie whole of the formations into four 

 great periods. Within the limits of each of these periods, the 



