126 THE WONDERS OF GEOLOGY. Lect. II. 



as rigidly prevail as in England, where the strata have 

 been subjected to violent and repeated physical revolutions. 



This is remarkably the case in Russia, where the Silu- 

 rian, Devonian, Carboniferous, and Permian systems of 

 rocks extend over immense regions, and are composed of 

 horizontal deposits of different ages, nearly all conformable 

 in position, and yet clearly separable from each other by 

 mineral characters and organic remains. Here then is 

 unequivocal proof, that some races of animals have disap- 

 peared and been succeeded by others, over enormously 

 extended areas, in which there has never been any great 

 physical catastrophe, nor the smallest eruption of plutonic 

 or volcanic matter.* 



These facts naturally suggest the inquiry, whether the 

 continuance of species may not be governed by some natural 

 law, in like manner as is the duration of the life of the 

 individuals of any given species. May not some species, 

 for example, be so constituted as to continue but for a few 

 hundreds or thousands of years — others for ages — while 

 other organisms may be endowed with a perpetuity of 

 reproduction through all time ? In this view of the subject, 

 species may have become extinct, simply because the pre- 

 destined term for the persistence of that peculiar form of 

 organism was expired; and this may have taken place 

 without any necessary relation to surrounding physical 

 conditions. In fine, may not the termination of the race, 

 like the death of the individuals, be the natural and inevi- 

 table result of their organization ? 



4. Animals extirpated by human agency. — But 

 leaving for the present the further consideration of this 



* " Geology of Russia," by Sir R. I. Murchison. These highly inte- 

 resting results, which are entirely due to the labours of this eminent 

 philosopher, have introduced a new and important element in all 

 speculations relating to the cause of the extinction of specie* in the 

 ancient geological periods. 



