Perpendicular, to ¼ to 1.
But, if non-weather-resisting,
½ to 1 TO 1 to 1,
The slope becoming flatter as the rock becomes softer and more easily disintegrated.
Friable rock, consisting of hard particles,
½ to 1 TO ¾ to 1.
Loose rock,
¼ to 1 TO 1 to 1.
Soft shaly limestone and the argillaceous rocks may not be permanently stable until the slope is,
1½ to 1 TO 2 to 1.