42 THE HARMONIES OF NATURE. 



could not have been called into existence if vegetable life, 

 favoured by peculiar atmospherical conditions, had not previously 

 cleansed the air of the pernicious gases with which it was satu- 

 rated during the early period of our earth's history. 



The ocean then rolled its waves over a far greater surface than 

 at present, for the large masses of land which now cover a con- 

 siderable part of the northern hemisphere were then still reposing 

 under the waters, which only appeared speckled here and there 

 with low and comparatively insignificant islands. Thus a mild 

 oceanic climate reigned far to the north, and its moist and 

 genial breath decked with a verdant robe even Spitzbergen 

 and Bear Island, where now winter with all his horrors holds 

 undisputed sway over the ice-bound soil. 



Besides moisture and warmth, the immense quantities of car- 

 bonic acid which was at that time mixed with the atmosphere, 

 contributed to promote vegetation ;' for this gas, so deleterious 

 to man and to the higher animals, constitutes, as is well known, 

 the chief food of plants, which have the power of separating it 

 into its constituent elements oxygen and carbon, restoring the 

 former to the air, and forming out of the latter the greater part 

 of their solid structure. 



The immensity of the coal-fields affords convincing proof of 

 the abundance of carbonic acid which filled the air at that 

 primeval epoch, for before its carbon became condensed by 

 vegetation, it evidently must have existed in a gaseous state ; 

 and thus also we see that the forests of this carboniferous period 

 first paved the way for a higher development of animal life, 

 by purifying the air and substituting oxygen for the deleterious 

 vapours with which it was loaded. 



Although the vegetable remains which constitute coal are 

 mostly in such a state of compression or transformation that no 

 trace of the original texture remains, yet the specimens which 

 one is able to distinguish from the mass plainly bear the cha- 

 racter of a swampy vegetation, and show that they must have 

 grown in submerged or at least extremely humid situations, 

 analogous to those in which the present peat or turf formation 

 takes place. 



These relics of an extinct world chiefly consist of cryptogamous 

 or non-flowering plants, such as arborescent ferns, and reed-like 

 calamites, stigmarias and lepidodendra, along with a few palms 



