352 ORTMANN— THE ALLEGHENIAN DIVIDE. [April 18, 



River fauna probably is a branch of this fauna has been indicated, 

 and the migration was in this case from the lower Ohio upstream. 

 The question remains whether the upper Ohio received also elements 

 from the upper Tennessee by another route, and this question is sug- 

 gested by the fact that the headwaters of Clinch and Holston rivers 

 on the one side and those of Big Sandy and New River approach 

 each other very closely and frequently interlock in the mountains. 



It is known (see Campbell, 1896, p. 670) that the headwaters of 

 the Big Sandy are preparing to capture the headwaters of Clinch 

 River in Tazewell Co., Va., in a region where the latter river has a 

 rich and characteristic fauna. The Big Sandy tributaries have 

 already reached the valley limestone and may have already deflected 

 some of the smaller tributaries of the Clinch. In the Najad-iauna. 

 of the Big Sandy (see p. 309) there is no evidence for this. But the 

 fact that a species of Pleurocera, PL unciale, is common to the 

 Clinch and the Big Sandy, possibly supports this assumption. 



There is also little evidence for a communication between the 

 upper Tennessee and New River except the existence of the Pleu- 

 rocerid-genus Anculosa in both systems and the presence of an 

 identical species of crayfish, Cambaras longulus. The two species 

 of N a jades j which are common to both systems, Elliptic» dilatatus 

 and Alasmidonta marginata, are without convincing value, since they 

 are found all over the interior basin, and of Elliptio dilatatus there 

 is surely quite a different, dwarfed race in the New River, while the 

 Clinch contains the normal form. In view of the tremendous con- 

 trast between the upper Tennessee and the New River faunas, it is 

 not very likely that there was any extended migration at any time 

 across this divide, or that there was any important shifting of this 

 divide. This is in accord with the general history of these streams. 

 According to Campbell (1894, p. no), the divide between New and 

 Holston rivers is a narrow col characteristic for a long-maintained 

 divide, and Hayes (1896, p. 330) says that the headwaters of the 

 Tennessee, running generally over softer rocks, had a tendency to 

 encroach northeastward upon the upper Kanawha system, but that 

 this tendency was counterbalanced by the fact that New River also 

 cut its own channel deeply into the (harder) rocks of its own trans- 



