152 ON THE ORIGIN OF COAL. 



occur.* The injection of volcanic trap into the 

 sea at some places, no doubt frequently interrupted 

 and destroyed the inhabitants of its waters, but 

 these disturbances being only local would not 

 interfere with the creatures living in distant seas ; 

 so that although certain races were partially cut 

 oflp at particular periods, in some localities, other 

 places existed where the same races of animals 

 escaped destruction, and re-peopled the seas, when 

 such again became fitted for animal life. 



The ancient seas, like those of the present day, 

 were doubtless peopled with beings fitted for the 

 conditions under which they lived, and when such 

 conditions changed the animals changed accord- 

 ingly. Some of these changes were no doubt 

 sudden, and others gradual. 



A great irruption of trappean rocks into the 

 sea, the rapid subsidence of its bottom to a great 

 depth, or the elevation of the bottom of the 

 ocean to the surface of the water, would be all 

 equally fatal to animal life in the respective 



* See Professor Sedgwick on North Wales. Quarterly 

 Journal of the Geological Society, No. I. p. 8. 



