AUTOCHTHONOUS SHEET

The rocks that have remained in their original place of formation, whether sedimentary, igneous or metamorphic or all of these are said to be "rigid" or autochthonous in the given orogenic belt and the mass together may be called an autochthon. For example, in Alps, the Aar massif or Augilles massif are a pre-Triassic crystalline basement forming the autochthon.