LAURENTIAN AND EA.^LY PALAEOZOIC. 



41 



beds of sandstone in the Upper Cambrian, carbonaceous 

 debris, which seems to be the remains of either aquatic 

 or land plants, is locally not infrequent. 



Referring to the land vegetation of the older rocks, it 

 is difficult to picture its nature and appearance. We 

 may imagine the shallow waters filled with aquatic or am- 

 phibious Rhizocarpean plants, vast meadows or brakes of 

 the delicate Psilophyton and the starry Protannularia 

 and some tall trees, perhaps looking like gigantic club- 

 mosses, or possibly with broad, flabby leaves, mostly cellu- 

 lar in texture, and resembling Algae transferred to the air. 

 Imagination can, however, scarcely realise this strange 

 and grotesque vegetation, which, though possibly copious . 

 and luxuriant, must have been simple and monotonous iji^ 

 aspect, and, though it must have produced spores and 

 seeds and even fruits, these were probably all of the types 

 seen in the modern acrogens and gymnosperms. 



" In garments green, indistinct in the twilight, 

 They stand like Druids of old, with voices sad and prophetic." 



Prophetic they truly were, as we shall find, of the 

 more varied forests of succeeding times, and they may 

 also help us to realise the aspect of that still older vege- 

 tation, which is fossilised in the Laurentian graphite ; 

 though it is not impossible that this last may have been of 

 higher and more varied types, and that the Cambrian and 

 Silurian may have been times of depression in the vegeta- 

 ble world, as they certainly were in the submergence of 

 much of the land. 



These primeval woods served at least to clothe the 

 nakedness of the new-born land, and they may have shel- 

 tered and nourished forms of land-life still unknown to 

 us, as we find as yet only a few insects and scorpions in 

 the Silurian. Tiiey possibly also served to abstract from 

 the atmosphere some portion of its superabundant car- 

 bonic acid harmful to animal life, and they stored up 



