9O SCIENCE SKETCHES, 



where the currents are more distinct ; third, those of 

 the creeks of the hill country ; fourth, those of the 

 elevated mountain streams which are subject to falls and 

 rapids." 



Farther on in the same paper, Professor Cope 

 reaches two important general conclusions, thus 

 stated by him : 



" I. That species not generally distributed exist in wa- 

 ters on different sides of the great water-shed. 



" II. That the distribution of the species is not gov- 

 erned by the outlet of the rivers, streams having similar 

 discharges (Holston and Kanawha, Roanoke and Susque- 

 hanna) having less in common than others having differ- 

 ent outlets (Kanawha, or Susquehanna and James). 



" In view of the first proposition, and the question of 

 the origin of species, the possibility of an original or sub- 

 sequent mingling of the fresh waters suggests itself as 

 more probable than that of distinct origin in the different 

 basins." 



Two questions in this connection are raised by 

 Professor Cope. The first question is this : " Has 

 any destruction of the river faunae taken place 

 since the first elevation of the Alleghanies, when 

 the same species were thrown into waters flowing 

 in opposite directions?" Of such destruction by 

 submergence or otherwise, Professor Cope finds 

 no evidence. The second question is, " Has any 

 means of communication existed, at any time, but 

 especially since the last submergence, by which 

 the transfer of species might occur?" Some 

 evidence of such transfer exists in the wide dis- 

 tribution of certain species, especially those which 



