OUTLINES OF GEOLOGY. 



87 



194. Similar evidence of frequent and successive changes 

 in the state and climate of the surface of the globe, are to be 

 found in the study of vegetable fossils. In the modem form- 

 ations we find little to show that the flora, even of the diluvial 

 period, was materially different from our own. But, even in 

 the higher strata of the superior order, a marked change is 

 to be detected, although not so much in the existing genera as 

 in the places where they occur : thus, the fossil flora of the 

 basins of ^London and Paris consists of palms, spice-bearing 

 laurels, and other plants manifesting the existence, in those 

 temperate latitudes, of a tropical climate. But if we consi- 

 der these plants in reference to the grand divisions of the 

 vegetable kingdom, the proportion among them is much the 

 same as at present. The dicotyledons were then, as now, 

 most numerous, and the cryptogamia the least so. 



On passing into the formations of the supermedial order, 

 this relation among the divisions of the vegetable kingdom 

 changes. Dicotyledons disappear, and the cryptogamia ex- 

 hibit themselves in greater abundance. One-third of the 

 species belong to the single family of ferns, and, with the cy- 

 cadse and coniferse, make up nearly the whole vegetation. 



In the medial order, the vegetables are remarkable for the 

 small variety which exists in their species, and for the great- 

 ness of their magnitude. All the vegetable fossils of this 

 order are comprised in no more than six families, while thos e 

 of the present day number 200. Of these six families, foui 

 belong to the cryptogamia, one to monocotyledons, and the 

 sixth probably to dicotyledons, although it is so different 

 from any of those of the present day as to leave a doubt as 

 to its classification. These six families include 258 fossil 

 species, in every hundred of which 92 are vascular crypto- 

 gamia ; while at the present day, in every hundred species no 

 more than four belong to that class. 



Another important difference is to be found in the fact 



