218 Prof. J. Van der Hoeven on the Succession and 
the Carboniferous period. The remaining species of this flora 
are referred to the Lycopodiaceze and Kquisetaceee*. The second 
period includes all the strata above the Coal-formation to the 
Upper Red Sandstone. In comparison to the first, the number 
of vegetable remains is only small; but, besides Acrogens, we 
observe amongst them Coniferous trees and Monocotyledons. 
In the third period, which comprehends the Oolitic and Creta- 
ceous group, Cycadeacee are predominant, and next to them 
follow ferns, the rest consisting chiefly of Monocotyledons. 
The fourth period embraces the Tertiary strata. It is only in 
this that remains of Dicotyledons are numerous. 
These results have been in part modified by new discoveries ; 
but even now it is certain that there is a great diversity between 
the species and genera, and even the greater divisions of a former 
and later vegetable and animal world. As to these modifications 
in the results of palzontological inquiry, it is now proved that 
the opinion of Cuvier, by whom the first apparition of land- 
mammals was stated to have been posterior to the Chalk period, 
must be given up. Already, during the lifetime of Cuvier, 
some few remains (lower jaws) of mammals were found in the 
slate of Stonesfield, which was proved to belong to the lower 
Oolitie strata, and consequently to be of a much more ancient 
date than the Chalk formation, on which the Tertiary strata are 
resting. In the last decennium, several new examples of mam- 
malian bones found in oolitic strata have been brought to light +; 
and Jow in the Upper Lias two molar teeth have been found, in 
1847, which Plieninger refers to a mammalian genus called by 
him Microlestes. 
But it seems that it would be overrating the value of these 
facts if we inferred from them that all great classes of the animal 
kingdom existed from the first beginning of life on the surface 
of the globe, that all were represented by different species, from 
the first geological periods till the modern era. In comparing 
the floree and faunz of different countries—a comparison which 
forms the fundamental part of a geography of plants and ani- 
mals—we must look chiefly to the dommating groups, to the 
families and genera which are distinguished by the larger num- 
ber of species. In the same manner, the characteristic features 
of different geological periods in relation to organic beings 
* To these must be added some Coniferous trees, more allied to Arau- 
cari than to any of our European firs. 
+ In the freshwater strata of Purbeck there were discovered, in 1856 
and the following years, a number of lower jaws, and even a fragment of 
a skull, of mammals, forming different genera, and partly allied to the in- 
sectivorous marsupial genus Amphitherium of Stonesfield. (See Sir Charles 
Lyell, Supplement to the fifth edition of a Manual of Elementary Geology, 
Lond. 1857, 8vo, pp. 15-27.) aie 
