Folds depend on the strength of rocks and intensity of forces because-
1. The elasticity of rocks largely affects the nature and magnitude of folding process.
2. The softer and more elastic rocks are subjected to intense folding while rigid and less elastic rocks are only moderately folded.
3. The compressional forces push two portions of the crustal rocks together and tend to shorten and thicken the crust.
4. Rocks that lie deep within the crust and are therefore under high pressure are generally ductile and particularly, susceptible to folding without breaking
