Soft rocks form folds while hard rocks form faults because –
1. Soft and elastic rocks are affected by compressional forces.
2. Rocks that lie deep within the crust and are therefore under high pressure are generally ductile and particularly susceptible to folding without breaking.
3. Whereas rock layers that are near the earth’s surface are too rigid to bend into folds.
4. If the tectonic force is large enough, these rocks will break rather than bend and faulting on rupture occur.
