CXVl PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



number of new species constantly discovered which have to be in- 

 serted between other aUied species already known, inferring that the 

 specific differences between each must by such additions tend to di- 

 minish continually, and that all species tend to be connected by more 

 and more close affinities. Thus, he argues, all differences gradually 

 disappear, and there results no greater difference between two 

 allied species than between varieties of the same species, and con- 

 sequently no difficulty in admitting that the difference which does 

 exist is not greater than what might be expected as the result of local 

 circumstances, modifying external forms, and thus practically pro- 

 ducing transmutation. Indeed he goes still further, and adopting an 

 infinite duration of time, and an infinite number of species, he argues 

 that there will ultimately be no perceptible difference at all between 

 two allied species. The following is his argument : — 



^' But, while the number of species thus tends to become infinitely 

 great, the extreme difference between man (let us suppose) at one end 

 and a zoophyte at the other end of the scale is constant and finite ; 

 hence the average difference between any two species tends to be- 

 come infinitely small ; multiplied by the number of species, it must 

 still be equal to di finite quantity ; and the product hem^ finite if the 

 first factor be infinity, the second must be zero.'^ 



This argument appears to involve a fallacy. If this infinite num- 

 ber of allied species is to prove the transmutation of one form into 

 another by showing that the difference between them is infinitely 

 small, it would be necessary to prove either that they had all existed 

 contemporaneously together, or that the allied forms immediately 

 succeeded each other. But when the author calls in the aid of long 

 geological epochs in which some of these closely allied forms existed 

 at long intervening periods, I cannot see how the question of trans- 

 mutation is thereby strengthened. If A, B, and C are the allied forms, 

 and A and C existed either together or in immediately succeeding 

 periods, and B, which is the connecting link to fill up the gap be- 

 tween them, is only found to exist after many millions of years, or 

 even only after the other two had died out, the theory of transmu- 

 tation cannot be supported by assuming the gradual change of A into 

 C, through the intervening form of B. If every possible gradation 

 of form existed in the fauna of one period and of one region, or of 

 successive periods and neighbouring regions, then indeed the advocates 

 of the transmutation theory might endeavour to maintain that all 

 these forms were only varieties of one type occasioned by the pecu- 

 liar conditions of life in which each was placed ; but this conclusion 

 is no longer vaUd when long periods have intervened between the 

 existence of one form and that of the other. The utmost argument 

 that could be drawn from such premises would be a confirmation of 

 the great doctrine of unity of plan in the creation of all organized life, 

 extending through all ages of the world. 



Another fallacy may, I think, be detected in the manner in which 

 Prof. Powell, after stating the arguments on both sides, points out 

 the real alternative. He says, " the only question is as to the sense 

 in which such change of species is to be understood ; whether indi- 



