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manner, been superseded by the knowledge that 

 thousands of species and genera, and even whole 

 families and orders, have disappeared and been suc- 

 ceeded by other and higher genera and species. So 

 also the belief that the creation of all these — ^planets, 

 plants, and animals as we now behold them — was the 

 summary work of a few days, has been supplanted by 

 the knowledge that our earth involves in the numerous 

 successions of her physical and vital aspects, as re- 

 vealed by geology, incalculable periods for their fulfil- 

 ment. And as this kind of knowledge has extended, 

 men of science have gradually begun to inquire into the 

 nature of the processes by which these changes have 

 been effected, and the laws by which these processes 

 are sustained and controlled. In this way the inves- 

 tigation has proceeded from the inorganic to the 

 organic world, from the rock-formations to the 

 plants and animals imbedded within them, and from 

 the succession of plants and animals to the methods 

 by which these successions are apparently connected. 

 Nothing could be more natural, and consequently 

 more philosophical, than this mode of procedure. 

 And as a gradual ascent in time from lower to higher 

 forms of life has been clearly established, and as 

 science has no evidence of other than the operation 

 of secondary forces in nature, so it seeks to ascribe 

 this ascent to this kind of causation. In other 



