92 



THE FAR PAST. 



of external conditions, under the influences of which many 

 of the silurian genera and species became extinct, and other 

 races were introduced specially adapted to the physical cir- 

 cumstances by which they were surrounded. 



In the Vegetable World we have now a greater exuber- 

 ance and variety of fucoids or sea-weeds ; marsh plants, 

 apparently related to the equisetums, reeds, and rushes ; 



1, Fucoid (Roxburghshire) ; 2, Zosteritea (Forfarshire) ; 3, Psilophyton (Canada), Dawson 



and unmistakable evidence of a terrestrial flora of no feeble 

 growth. Ferns of rare beauty (adiantites), club- moss- 

 like stems of gigantic growth (lepidodendra), and fruit 

 cones (lepidostrolms\ are by no means uncommon, and 

 every year is adding some new feature to a flora which a 

 dozen years ago was set down as having no existence. 



corroboration of the idea of glacial influences an hypothesis which seems 

 at first sight extremely probable, though requiring for its final demon- 

 stration a much more protracted and careful examination than the several 

 phenomena have yet received from geologists. 



