640 HISTORY OF GEOLOGY. 



hypothesis. Are these new species created by the 

 production, at long intervals, of an offspring different 

 in species from the parents ? Or are the species so 

 created produced without parents ? Are they gra- 

 dually evolved from some embryo substance ? or do 

 they suddenly start from the ground, as in the 

 creation of the poet? 



Perfect forms 



Limbed and full-grown : out of the ground up rose 



As from his lair, the wild beast where he wons 



In forest wild, in thicket, brake, or den ; . . . 



The grassy clods now calved ; now half appeared 



The tawny lion, pawing to get free 



His hinder parts ; then springs as broke from bounds, 



And rampant shakes his brinded mane ; &c. &c. 



Paradise Lost, B. vii. 



Some selection of one of these forms of the 

 hypothesis, rather than the others, with evidence 

 for the selection, is requisite to entitle us to place it 

 among the known causes of change which in this 

 chapter we are considering. The bare conviction 

 that a creation of species has taken place, whether 

 once or many times, so long as it is unconnected 

 with our organical sciences, is a tenet of Natural 

 Theology rather than of Physical Philosophy (IA). 



2. Extinction of Species. With regard to the 

 extinction of species, Mr. Lyell has propounded a 

 doctrine which is deserving of great attention here. 

 Brocchi, when he had satisfied himself, by exami- 

 nation of the Sub- Apennines, that about half the 

 species which had lived at the period of their depo- 



