VI.] SPECIES AND TIME. 151 



strongly in their favor when we consider liow much they 

 tell against the theory of Mr. Darwin. The last-named 

 author only remarks that " many of the elements in the cal- 

 culation are more or less doubtful." " and Prof. Huxley " 

 does not attempt to refute Sir W. Thomson's arguments, 

 but only to show cause for suspense of judgment, inasmuch 

 as the facts may he capable of other explanations. 



Mr. Wallace, on the other liand," seems more disposed 

 to accept them, and, after considering Sir William's objec- 

 tions and those of Mr. Croll, puts the probable date of the 

 beginning of the Cambrian deposits '' at only twenty-four 

 million years ago. On the other hand, he seems to consid- 

 er that specific change has been more rapid than generally 

 supposed, and exceptionally stable during the last score or 

 so of thousand years. 



Now, first, with regard to the time required for the evo- 

 lution of all organic forms by merely accidental, minute, 

 and fortuitous variations, the useful ones of which have 

 been preserved. 



Mr. Murphy '* is distinctly of opinion that there has not 

 been time enough. He says : " I am inclined to think that 

 geological time is too short for the evolution of the higher 

 forms of life out of the lower by that accumulation of im- 

 perceptibly slow variations, to which alone Darwin as- 

 cribes the whole process." 



" Darwin justly mentions the greyhound as being equal 

 to any natural species in the perfect coordination of its 

 parts, * all adaj)t(Hl for extreme fleetness and for running 

 down weak prey.' " " Yet it is an artificial species (and 

 not physiologically a species at all)^ formed by long-con- 



'0 " Origin of Species," 5th edit., p. 354. 



J' Sec his address to the Geological Society, on February 19, 1869. 



'2 See Nature, vol. i., p. 399, February 17, 1870. 



'•'' Ibid., vol. i., p. ATy{. 



'* " Habit and Intelligence," vol. i., p. 344. 



