354 M: Brongniart 07i the Vegetation of 



The first period in fact corresponds to the Transition Jbrrna- 

 tions, among which some geologists include the Coaljbrmation. 



The second comprehends the greater part of the inferior sedi- 

 mentary Jbrmaticnis. 



The third embraces the end of these Jhrmations^ and the middle 

 sedimentary formations. 



TJie fourth corresponds exactly to the Tertiary or upper sedi- 

 mentary formations. 



It ought also to be observed, that the limits of these periods 

 appear connected in a particular manner with the geological 

 phenomena which have given rise to the strata of the globe. In 

 fact, the strata which contain the remains of vegetables, which 

 we consider as belonging to the same period, are almost always 

 separated from those which belong to another period of vegeta- ' 

 tion, by formations which seem entirely destitute of land vege- 

 tables, and whose epoch of formation corresponds to a period of 

 time during which the earth was perhaps completely covered 

 by the sea, or almost entirely destitute of terrestrial vegetables. 



Thus, the first period, or that of the coal deposit, is sepa- 

 rated from the second, which corresponds to the variegated 

 sandstone, by the old red sandstone, in which no vegetables have 

 been observed, and by the magnesian or alpine limestone which 

 has hitherto presented only marine vegetables. 



The second period is separated from the third, which com- 

 mences at the keuper and lias, by the shell-limestone or muschel- 

 kalk, which is also almost entirely destitute of fossil vegetables. 



Between the third period, which ends with the upper beds of 

 the Jura limestone, and the fourth, which corresponds to the up- 

 per sedimentary or tertiary formations, occurs the Chalk, in the 

 mass of which no other vegetables have hitherto been found than 

 a few marine plants. 



This supposition of a complete or almost complete interrup- 

 tion of vegetation at the surface of the globe, between two of 

 the periods of vegetation which we have admitted, is so much 

 the more probable, that there exists no species common to two 

 successive periods. Every thing is different in them, and the 

 idea cannot be rejected, that a new vegetation, arising under in- 

 fluences different from those which previously existed, has occu- 

 pied the place of the old vegetation. 



