SILURIAN ERA. 



85 



period, nor to define with certainty the external conditions 

 to which its flora and fauna would be necessarily sub- 

 jected. 



When we turn to its biological aspects, the outline, 

 though far from complete, is at least, as far as it goes, 

 homogeneous and intelligible. Fucoids or fucus-like sea- 

 weeds, some carbonaceous fragments of unknown stems, 

 spore-like organisms, apparently from land plants, and a 

 few lepidodendroid twigs that may have belonged to some 

 ancient form of club-moss, are nearly all we know of the 

 silurian Flora ; though, judging from the extent of an- 

 thracite deposits in various regions, vegetation (aquatic and 

 terrestrial) must in certain centres have existed in some 



1. ;, FucoicU Ci-aziana and Choudrites >,?) ; 3, 4, Lyccpodites Lepidodendroid twigs from. 

 the Upper Silurians of Lanarkshire . 



exuberance. On the whole, the silurian Flora is of a very 

 lowly character, and its scanty fragments find their nearest 

 affinities in the sea-weeds, liver-worts, and club-mosses of 

 existing nature. Of course, the imperfection of the geolo- 

 gical record is fully and frankly admitted, for it cannot be 



