158 EXPLANATIONS. 



way before the application of this rule, and it 

 must be seen that what they call new species are 

 but variations upon the old. What, then, will re- 

 main to be done, before the theory of progressive 

 development be adopted } Only, as the candid 

 reader will readily surmise, that the cultivators of 

 science should allow themselves to follow the dic- 

 tates of reason, against the behests of prejudices 

 unworthy of them and of their age. 



Time is the true key to difficulties regarding 

 appearances of determinateness in species. Few 

 of us, not even geologists, have ever realized in 

 our minds the extent of time which has elapsed 

 since the beginning of life upon this;globe. Mr. 

 Lyell, without intending to favour the develop- 

 ment theory, lends us powerful testimony on this 

 point. After showing reason to believe, that about 

 thirty -five thousand years have passed since the 

 Niagara began to cut down the rock through which 

 it flows, during which time the living mollusks, 

 whether marine or terrestrial, are proved to have 

 undergone no change, he thus proceeds — " If such 

 events can take place, while the zoology of the 

 earth remains almost stationary and unaltered, 

 what ages may not be comprehended in those sue- 



