M. De CandoUe on Fossil Vegetables. 101 



thinks it necessary to suppose, that the atmosphere then con- 

 tained a nuich larger proportion of carbonic acid gas than it dues 

 now. As it might happen, there was then much less mould, 

 plants must needs have lived by absorbing, through the leaves, 

 and appropriating to themselves, much carbon taken from the 

 air. ]\I. Th. de Saussure has demonstrated, that a proportion 

 of two, three, four, and even eight, per cent, of carbonic acid 

 gas in the air, was favourable to vegetation. In this method the 

 gigantic height of the plants of the first period might be ex- 

 plained. The simultaneous existence of many reptiles, and the 

 absence of the mammalia, also accords with this hypothesis. 

 After an epoch so distant as this, the flourishing of so many ve- 

 getables, and perhaps other causes, may have greatly reduced 

 the quantity of carbonic acid gas contained in the atmosphere, 

 at the same time augmenting the thickness of the soils that are 

 favourable for the vegetation of the plants of the present time. 



The authors of the first volume of the Fossil Flora of Eng- 

 land, draw our attention to the singular fact, that the coal-mines 

 of Canada and Baffin's-Bay contain plants analogous to those of 

 other coal-mines, and consequently to those which now flourish 

 under the equator. Mastodons, and other animals analogous to 

 tho.se of intertropical climates, have also lived at Melville Island, 

 close to the pole. The diff'erence of temperature, from that of 

 the present day, may be attempted to be explained in different 

 methods, and, among others, by the gradual and continued re- 

 frigeration of the internal heat of the globe ; but the authors of 

 the Fossil Flora, with justice, remark, that the plants of equa- 

 torial countries require light, and that equably distributed, as 

 much as heat. There are very few vegetables which can with- 

 stand the privation of light for a few months. This is one of 

 the causes which prevents the progress of plants of temperate 

 regions towards the nortj), and which prevents them from thriv- 

 ing in the hottest greenhouses in high latitudes. 



It must have been '.he same with the fos.sil plants which are 

 analogous to those of our equatorial regions. Besides, as the 

 inequality of our days depends upon the position of the earth 

 to the sun, it would appear that, ere tree-ferns could flourish 

 where the pole now is, the inclination of the ecliptic must have 

 been different. 



