The document discusses different types of unconformities: - Angular unconformity occurs when rock layers above and below are not parallel due to erosion and deposition over a long period of time with changes in bedding orientation. - Nonconformity separates older crystalline rocks from overlying younger sedimentary or volcanic rocks, representing a long period of erosion. - Disconformity has parallel bedding above and below, separated by erosion over some time. - Local unconformity is similar to a disconformity but represents only a short period of non-deposition over a small area.