CARBONIFEROUS ERA. 101 



in the distribution of land and water shallower seas larger 

 rivers and estuaries wide, far- stretching swampy lands ; and 

 with these, new ocean-currents, a more genial and equable 

 climate, and, as a concomitant, a more exuberant exhibi- 

 tion, and over wider areas, of vegetable and animal life. 

 In some regions, but by no means over the whole world.' 

 the transition from the one period to tlte -otXai" seems to 

 have taken place through convulsive -energy ; -aikl hence 

 in these regions comparatively few of 'ihe'fOrms b* the 1 eld 

 red sandstone survive, or pass into the carboniferous era. 

 As in every other period, the new forms come slowly and 

 gradually on the stage, attain their " culminating point," or 

 period of greatest variety, size, and numbers, and then 

 gradually or quickly decline, according to the continuity of 

 the conditions by which they are surrounded. In the 

 vegetable world we have now a most exuberant Mora so 

 exuberant that it is but faintly paralleled by the rankest 

 growth of the tropical jungle. To account for this extra- 

 ordinary development of plant-life, over such wide and 

 diversely situated regions of the globe, various hypotheses 

 have been offered, such as a larger percentage of carbonic 

 acid gas in the atmosphere the greater effect of the earth's 

 central heat change in the earth's axis of rotation, so as to 

 bring the coal-bearing areas within the tropics and greater 

 eccentricity of the earth's orbit, so as to have brought the 

 globe periodically nearer to the sun's influence ; but as we 

 have not in the mean time* a shadow of proof for such 

 abnormal causes, and much evidence to the contrary, we are 

 bound by sound induction to seek for the explanation in 



* We say in the mean time; for the recurrence of colder and warmer 

 cycles over the northern hemisphere, as evinced by the geological record, 

 is clearly the result of some great cosmical law, depending either on 

 telluric or on solar influences, and, as such, must sooner or later be 

 satisfactorily determined. See Concluding Chapter "The Law," Sec- 

 tion 6. 



