If an “Angle Line” defines the straight Iine from the center of a projection net to the middle point of great circle (arc) which represents the dip of the planar direction on an equal-angle projection net, the dip of geological separation is indicated by the Angle Line as well as by great circle.
The “Angle Line”, may enable us to classify the rock slopes ultimately into six types: Dip Slope Type I (φ>β), Dip Slope Type II (α>β>φ), Dip Slope Type III (β>α), Scarp Slope Type I (φ>90-β), Scarp Slope Type II (α>90-β>φ), Scarp Slope Type III (90-β>α), Where, α=the dip of the rock slope, β=the dip of main geological separation in the rock slope, φ=the frictional angle of sliding.
My field reseach on the rock slopes along the Kuji Glen evidently shows that it is only the rock slopes of our Dip Slope Type II that have scars of large failures on them. This proves that classification of rock slopes on the basis of the Angle Line is effective for preventing rock slope failures.