Boulder deposits and the retreat of mountain slopes, or ' gully gravure' revisited.

Observations on mountains composed chiefly of shale and capped with Tuscarora Sandstone in the Valley and Ridge province of southwest Virginia suggest that slopes retreat by a process similar to but different from Bryan's (1940) gulley gravure. This process probably is common wherever large resistant clasts are transported downslope over less resistant bedrock. Lateral migration of stream valleys has been shown to take place on mountain piedmonts under similar circumstances, but this study suggests that such migration may also take place on the upper slopes of mountains in hollows where water flow may be significant only a few times per century. -from Author