THE CARBONIFEROUS FLORA. 



139 



grounds, that the carboniferous atmosphere differed from 

 that of the present world in this way, or in the presence 

 of more carbonic acid — a substance now existing in the 

 very minute proportion of one thousandth of the whole — 

 a quantity adapted to the present requirements of vege- 

 table and animal life, but probably not to those of the 

 coal period. 



Thus, if we inquire as to any analogous distribution of 

 plants in the modern world, we find this only in the warm- 

 er insular climates of the southern hemisphere, where 

 ferns, lycopods, and pines appear under forms some- 

 what akin to those of the Carboniferous, but mixed with 

 other types, some of which are modern, others allied to 

 those of the next succeeding geological ages of the Meso- 

 zoic and Tertiary ; and under these periods it will be 

 more convenient to make comparisons. 



The readers of recent English popular works on geol- 

 ogy will have observed the statement reiterated that a 

 large proportion of the material of the great beds of bi- 

 tuminous coal is composed of the spore- cases of lycopo- 

 diaceous plants — a statement quite contrary to that re- 

 sulting from my microscopical examinations of the coal 

 of more than eighty coal-beds in Nova Scotia and Cape 

 Breton, as stated in "Acadian Geology" (page 463), and 

 more fully in my memoir of 1858 on the "Structures in 

 Coal," * and that of 1866, on the " Conditions of Ac- 

 cumulation of Coal."f The reason of this mistake is, 

 that an eminent English naturalist, happening to find in 

 certain specimens of English coal a great quantity of re- 

 mains of spores and spore-cases, though even in his speci- 

 mens they constitute only a small portion of the mass, 

 and being apparently unacquainted with what others had 

 done in this field, wrote a popular article for the " Con- 

 temporary Keview," in which he extended an isolated and 



* " Journal of the Geological Society," vol. xv. 



f Ibid., vol. xxii. 



