THE ANNALS 



AND 



MAGAZINE OF NATURAL HISTORY. 



[SECOND SERIES.] 

 No. 32. AUGUST 1850. 



VII. — Chronological Exposition of the Periods of Vegetation and 

 the different Floras which have sticcessively occupied the surface 

 of the .Earth. By M. Adolphe Brongniart*. 



If, after having studied fossil plants in regard to their organiza- 

 tion, so as to determine their relations to the vegetation now 

 existing, without attending to the geological position they occupy, 

 we compare the different forms which have inhabited the surface 

 of the earth at different epochs of its formation, we shall perceive 

 that great differences present themselves in the nature of the 

 vegetables which have been successively developed, and have re- 

 placed those destroyed by the revolutions of the globe and the 

 changes in the physical condition of its surface. 



These are not merely specific differences, slight modifications 

 of the same types ; more frequently they are profound differences, 

 in such sort that new genera or families take the place of genera 

 and families destx'oyed and completely distinct ; or a numerous 

 and varied family is reduced to a few species, whilst another, 

 poorly represented by a few rare individuals, becomes all at once 

 numerous and predominant. 



This is what strikes us most commonly in passing from one 

 geological formation to another; but in considering these trans- 

 formations collectively, a more general and more important result 

 presents itself in an unmistakeable manner, namely the predo- 

 minance in the most ancient times of Acrogenous Cryptogamic 

 plants (Ferns and Lycopodiaceae) ; later, the predominance of 

 Gymnospermous Dicotyledons (Cycadeae and Coniferse) without 

 the admixture yet of a single Angiospermous Dicotyledon ; finally, 

 during the cretaceous formation, the appearance and soon the 

 predominance of Angiospermous plants, both Dicotyledons and 

 Monocotyledons. These very remarkable differences in the 



* From the Ann. des Sc. Naturelles, Botanique, 3 Ser. vol. xi. p. 285, 

 May and June 1849. Translated by Arthur Henfrev, F.L.S. 

 Ann. S^ Mag. N. Hist. Ser. 2. Vol. vi. ' 6 



