fall line

1. The zone or boundary between resistant rocks of older land and weaker strata of plains. 2. The line indicated by the edge over which a waterway suddenly descends, as in waterfalls.

Related terms:

• shear line
• squall line
• Anticlinal line
• flowage line
• fall wind
• wind-shift line
• hinge line
• instability line
• prefrontal squall line
• cocurrent line