LAURENTIAN AND EARLY PALAEOZOIC. 17 



fishes of that age. "How I wish I could sit under its 

 shade ! " was the smiling reply of the great zoologist ; and 



en we think of the great accumulations of Laurentian 



bon, and that we are entirely ignorant of the forms 

 ind structures of the vegetation which produced it. we 

 can scarcely suppress a feeling of disappointment. Some 

 things, however, we can safely infer from the facts that 



known, and these it may be well to mention. 



The climate and atmosphere of the Laurentian may 

 have been well adapted for the sustenance of vegetable 

 life. We can scarcely doubt that the internal heat of the 

 earth still warmed the waters of the sea, and these warm 

 waters must have diffused great quantities of mists and 

 vapours over the land, giving a moist and equable if not a 

 very clear atmosphere. The vast quantities of carbon di- 

 oxide afterwards sealed up in limestones and carbonaceous 

 beds must also have still floated in the atmosphere and 

 must have supplied abundance of the carbon, which con- 

 stitutes the largest ingredient in vegetable tissues. Under 

 these circumstances the whole world must have resembled 

 a damp, warm greenhouse, and plants loving such an at- 

 mosphere could have grown luxuriantly. In these cir- 

 cumstances the lower forms of aquatic vegetation and 

 those that love damp, warm air and wet soil would have 

 been at home. 



If we ask more particularly what kinds of plants 

 might be expected to be introduced in such circumstances, 

 we may obtain some information from the vegetation of 

 the succeeding Palaeozoic age, when such conditions still 

 continued to a modified extent. In this period the club- 

 mosses, ferns, and mare's-tails engrossed the world and 

 grew to sizes and attained degrees of complexity of struc- 

 ture not known in modern times. In the previous Lau- 

 rentian age something similar may have happened to 

 Algae, to Fungi, to Lichens, to Liverworts, and Mosses. 

 The Algge may have attained to gigantic dimensions, and 



