ARRANGEMENT OF FOSSIL PLANTS. 



171 



ness, and very fine, or divided in a very simple manner, it is 

 probable that they indicate the fern tribe, whether simple, 

 as in the fossil genus tceniopteris, or reticulated, as in the 

 modern genus meniscium. If the veins are of unequal 

 thickness, and so branched as to resemble the meshes of 

 a net, we have a sign of dicotyledonous structure that 

 seldom misleads us. finally, if no veins are to be found, 

 an opinion must be formed, not from their absence, but 

 from other circumstances. If the leaves are small, their 

 absence may be due to incomplete development, but if they 

 are large and irregularly divided, we may have an indication 

 of some kind of marine plant. When the leaves are small 

 and densely imbricated, they are generally considered to 

 belong either to lycopodiacece or conifercB ; but there is so 

 little to distinguish these families in a fossil state, that there 

 is scarcely any means of demonstrating to which of these 

 such genera as lycopodites, lycopodendron, juniperites, taxites, 

 &c., and the like, actually belong. 



ARRANGEMENT OF FOSSIL PLANTS. M. Adolphe Brong- 

 niart has divided the vegetation of the ancient earth into 

 four periods. The first commences with the earliest traces 

 of vegetable life, and terminates with the carboniferous 

 epoch; the second concludes with the triasic; the third 

 comprises the oolite and chalk ; and the fourth the tertiary 

 period. In his Prodrome d'une Histoire des Vegetaux Fossiles, 

 the following comparative table of the extinct and living 

 classes of plants is given : 



First Second Third Fourth T . . 

 Period. Period. Period. Period. ^ mn S' 



Cryptogamise celluloses 



vasculosse . 



Phanerogamic gymnospermise 

 Monocotyledoniae . 

 Dicotyledonise . 

 Indeterminate 



222 



10 



22 



This table has now been published some years, during 

 which several new species have been discovered; but the 

 general proportions remain much the same. 



REMARKS OF COUNT STERNBERG. These four periods 

 Count Sternberg reduces to three, by uniting the second and 



