368 ORTMANN— THE ALLEGHENIAN DIVIDE. [April 1 8, 



gheny drainage it goes way up into the headwaters : 21 it is in the 

 upper Youghiogheny and in the upper Tygart and Buckhannon 

 rivers. Thus it closely approaches the divide in the whole northern 

 section of the upper Ohio drainage. On the eastern side, it is also 

 found close up to the divide in the Susquehanna, Potomac, James, 

 and Roanoke drainages. 22 The eastern and western ranges are 

 consequently in rather close contact along the northern part of 

 the Alleghenian divide, from the uppermost Allegheny River to the 

 region of the headwaters of the Monongahela, Potomac and James. 

 But the close approach is most marked in central Pennsylvania, in 

 Cambria, Indiana, and Westmoreland counties. Here this species 

 is common in all small streams running east and west from the 

 divide, and, for instance, the locality in Cush-Cushion Creek, be- 

 longing to the Susquehanna, is not more than twenty or twenty-five 

 miles from the nearest localities in the Allegheny drainage (Creek- 

 side, Homer, Goodville). 



This is just in the region where the Susquehanna drainage has 

 largely encroached upon the drainage of the Allegheny River, and 

 where stream capture has taken place. Although Davis (1889, P- 

 248) believes that this was accomplished chiefly in Pretertiary times, 

 there is no objection to the assumption that to a lesser degree this 

 process continued in the headwaters also during the Tertiary, in fact, 

 that it is going on at present. If this is admitted, there is no diffi- 

 culty in imagining that with the waters part of the fauna of the 

 western streams was taken over into the eastern drainage, and since 

 Strophitus inhabits these smaller western streams, it might thus have 

 crossed the divide, in this region, by the help of stream capture. 



21 Potato Cr., Smethport, McKean Co. ; Little Mahoning Cr., Goodville, 

 Indiana Co. ; Crooked Cr., Creekside, Indiana Co. ; Yellow Cr., Homer, In- 

 diana Co. ; Blacklegs Cr., Saltsburg, Indiana Co. ; Beaver Run, Delmont, 

 Westmoreland Co. ; Loyalhanna Riv., Ligonier, Westmoreland Co. ; Quema- 

 honing Cr., Stanton's Mill, Somerset Co. ; all in Pa. 



22 For instance: in the system of the Susquehanna: Cush-Cushion Cr., 

 Greene Twp., Indiana Co. ; Chest Cr., Patton, Cambria Co. ; Swartz Run, Ash- 

 ville, Cambria Co. ; Beaver Dam Cr., Flinton, Cambria Co. ; Raystown Branch 

 Juniata Riv., Everett and Mt. Dallas, Bedford Co. ; all in Pa. ; South Branch 

 Potomac Riv., Romney, Hampshire Co., W. Va. ; James drainage : Calf 

 Pasture Riv., Goshen, Rockbridge Co., Va. ; Roanoke drainage : Mason Cr., 

 Salem, Roanoke Co., Va. 



