EXTINCTION AND CEEATION. 195 



and always with a determinate relation to pre-existing 

 vitality. 



[Extinction and Creation of Species.] 



In adopting the terms "extinction" and "creation," 

 we must not fall into the common, but mistaken, notion, 

 that the Flora and Fauna of one period were utterly extin- 

 guished before the commencement of the next. There are 

 no such extinctions and re-creations in nature. Just as the 

 physical change from one formation to another was sudden 

 or gradual, so a less or greater number of genera and spe- 

 cies passed from the older to the newer epoch. In some 

 localities the change was sudden and entire, in others it 

 was gradual so gradual that we can hardly trace the line 

 of demarcation. Take, for example, the old red sandstone 

 of the British Islands. What a vast difference between the 

 fauna of Siluria proper, and that of the old red sandstone 

 of Caithness ! The break seems decided and impassable, 

 and yet when we turn to Forfarshire and Lanark we find 

 silurian genera and species passing up into the old red 

 sandstone and completing the continuity, which, to a Caith- 

 ness geologist, would have seemed to be entirely rent 

 asunder. Again, what a marked difference between the 

 fauna of the Forfarshire and Caithness beds between 

 that of the Hereford sandstones, and that of the limestones 

 of Devon ! and yet when we pass to the old red sandstone 

 region of Russia we find these different stages fused and 

 equalised into one homogeneous Life-system. What was 

 broken up into different stages by physical irregularities in 

 the area of Great Britain was left to evolve itself gradually 

 and continuously in the region of Russia. We must exa- 

 mine more and know more before we hasten to such sweep- 

 ing conclusions as general extinctions and creations ; and 



