gO 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: — 
“J. That species not generally distributed exist in wa- 
ters on different sides of the great water-shed. 
“TI. 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 faune 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 
