I9I3-] ORTMAXX— THE ALLEGHEXIAX DIVIDE. 355 



ing River is yet obscure. As we have seen, Leverett unites it with 

 the Preglacial lower Ohio. But the fauna of the river, especially 

 of the X a jades, strongly points to the fact that Licking River has a 

 similar history to that of the Kanawha and Monongahela, that is to 

 say, that it was in Preglacial times a nortiizcard flozcing stream, 

 which might have belonged to the old Erigan River (see above, p. 

 349), and that it had no connection with the lower Ohio and Ten- 

 nessee-Cumberland. And indeed this is the assumption made by 

 Tight (1903, see map, pi. 1), who gives to the Licking and Kentucky 

 rivers (under the name of Cincinnati River) 3. northward flow in 

 Preglacial times. 



Thus, in this case, zoögeographical evidence is in favor of Tight's 

 assumption, and this is an interesting instance, where zoogeography 

 contributes to the solution of a physiographical question. 14 



We have repeatedly emphasized, that the upper Ohio fauna is a 

 unit, and rather uniform all over the terrritory it occupies, with the 

 only qualification, that it slowly depauperates in an upstream direc- 

 tion. This is true, in the first line, of the Na jades, but it may be 

 correct also for certain Pleuroceridcc, at least such forms which 

 follow mainly the large rivers (certain species of Pleuroccra, as for 

 instance, PL canaliculatum). But in other groups, some minor dif- 

 ferences within the upper Ohio fauna are noticed. Some evidence 

 of this is seen in the Pleuroceridae of the smaller rivers, the Alle- 

 gheny, Monongahela, Kanawha, Big Sandy and Licking, each of 

 which has different species of Pleuroccra and Goniobasis (provided 

 such are present at all). But these conditions require further study, 

 chiefly with regard to the affinities of these forms. But it is inter- 

 esting to note, that it seems that the conditions known to exist among 

 the crayfishes are duplicated here. 



In the case of the crayfishes, I have pointed out (1906), that 

 there are two different species in the upper Ohio drainage, and that 



14 This should be studied farther, chiefly with regard to the additional 

 question regarding Kentucky River : If Tight's and our view is correct, Ken- 

 tucky River should conform in its fauna to that of Licking River and the 

 upper Ohio in general ; if it belongs, however, to the lower Ohio, it should 

 contain elements of the Cumberlandian fauna. Unfortunately the Kentucky 

 fauna is practically unknown. 



