220 Darwin, and after Darwin. 



types ? Even if such a case stood alone, it would be 

 strongly suggestive of error on the part of the special 

 creation theory. But let us take another case, this 

 time from fresh-water faunas. 



Although the geographical distribution of fresh- 

 water fish and fresh-water shells is often surprisingly 

 extensive and apparently capricious, this may be 

 explained by the means of dispersal being here so 

 varied not only aquatic birds, floods, and whirl- 

 winds, but also geographical changes of water-shed 

 having all assisted in the process. Moreover, in 

 some cases it is possible that the habits of more 

 widely distributed fresh-water fish may have origin- 

 ally been wholly or partly marine which, of course, 

 would explain the existing discontinuity of their ex- 

 isting fresh-water distribution. But, be this as it 

 may (and it is not a question that affects the issue 

 between special creation and gradual evolution, since 

 it is only a question as to how a given species has 

 been dispersed from its original home, whether or 

 not in that home it was specially created), the 

 point I desire to bring forward is, that where we 

 find a barrier to the emigration of fresh- water 

 forms which is more formidable than a thousand 

 miles of ocean a barrier over which neither 

 water- fowl nor whirlwinds are likely to pass, and 

 which is above the reach of any geological changes 

 of water-shed, where we find such a barrier, we 

 always find a marked difference in the fresh-water 

 faunas on either side of it. The kind of barrier 

 to which I allude is a high mountain-chain. It 

 may be only a few miles wide ; yet it exercises a 

 greater influence on the diversification of specific 



