EARTH FEATURES SHAPED BY RUNNING WATER 177 



crossed the Blue Ridge of the time through similar water gaps 



(Fig. 185, map, and Fig. 186). The Potomac of that time was, 



however, the more 



deeply intrenched, 



and possessing an 



advantage in slope 



it was able to 



advance the divide 



at the head of its 



tributary, the 



Shenandoah, into 



FIG. 186. Section to illustrate the history of Snickers 

 Gap. 



the territory of Beaverdam Creek. Thus the beheading of the 

 Beaverdam by the Shenandoah was accomplished (Fig. 185, second 

 map) and its upper waters annexed to the Potomac system. 

 With the subsequent lowering of the general level of the country 

 which yielded the present Shenandoah Plain, the former water gap 

 of Beaverdam Creek was abandoned of its stream at a high level 

 in the range. Known as Snickers Gap, it may serve as a type of 

 the " wind gaps " of similar origin which are not altogether un- 

 common in the Appalachian Mountain system (Fig. 186). 



Character profiles. For humid regions the landscapes possess 

 characters which, speaking broadly, depend upon the stage of the 

 erosion cycle. For the earliest stages the straight line enters 

 as almost the only element in the design ; as the cycle advances 

 to adolescence the rounded forms begin to replace the angles of 



/ YOUTH \ I ADOLESCENCE^. 



FIG. 187. Character profiles of landscapes shaped by stream erosion in humid 



climates. 



N 



