352 UNIVERSITY OF VIRGINIA PUBLICATIONS 



Since the headwaters of the streams of the Northern Appalachians 

 which continue across the Blue Ridge are identical in character with 

 those streams which do not, it seems entirely evident that all have had 

 the same initial history, and that the more important streams including 

 the three principal tributaries of the Shenandoah, which followed the 

 direction of greatest continental slope, continued their courses to the 

 Atlantic across the position the Blue Ridge now occupies. There could 

 hardly have been an exception to this in the case of an important stream 

 immediately following the Appalachian revolution. 



The relation of North Fork, North River, and Middle River to the 

 Great Valley and the Alleghany Ridges on the one hand, and to the Blue 

 Ridge and Massanutten Mountain on the other, is entirely different (pi. I) . 

 Initially the relation of the streams to these physiographic features must 

 have been the same, but owing to geologic conditions chiefly structure 

 and lithologic types, only the more able boched streams, which made 

 up the original consequent drainage of the region, have been able to 

 maintain their courses across the barriers east of the hmestone belt of the ■ 

 Great Valley. 



The varying size and distribution of the many wind gaps in the Blue 

 Ridge and the relation of the gaps to existing drainage lines is very sig- 

 nificant. It will be observed by consulting the map, pi. I, of the present 

 drainage of the region, that opposite the point where any one of the im- 

 portant tributaries enters the Shenandoah there is a more or less promi- 

 nent wind gap in the Blue Ridge. In the case of North Fork which 

 enters the Valley through Brock's Gap near Broadway two barriers were 

 encountered, Massanutten Mountain and the Blue Ridge, and in both 

 cases wind gaps afford evidence of its antecedent course across the moun- 

 tains after which it probably continued to the Atlantic through the Rappa- 

 hannock. Near New Market this stream changes its course to the north- 

 east opposite a well developed wind gap in Massanutten Mountain (pi. 

 Ill, fig. 1). If it continued its course through this gap and thence in the 

 same direction to the Blue Ridge it would pass through another similar 

 gap. Instead of following this course it flows in a northeasterly direction 

 along the northwestern foot of Massanutten Mountain to the vicinity of 

 Strasburg where it turns again in an easterly direction and enters the 

 Shenandoah at Riverton opposite the largest and best developed wind 

 gap in the Blue Ridge along the Shenandoah Valley region. 



Middle and North rivers, uniting at Mt. Meridian before they join 

 the Shenandoah at Port Republic, likewise flow in a direction which would, 

 if continued, pass through a wind gap in the Blue Ridge. 



