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       A sheet or pile of rocks that has moved considerable distance from the place where it was formed; in an orogenic belt, where it lies over an autochthonous block which has stayed in its own place. A surface of decollement separates the lower autochthon and an upper allochthon. Many Alpine and Himalayan nappes have formed in this manner by large scale mass transport. Sometimes, there is little deformation in the allochthonous nappes despite the long distance over which they have moved. The diagrams produced here are that of window and klippe, ramp and flat, and stretching lineations and stylolites together with syntectonic crack seal antitaxial, syntaxial, composite or stretched crystal veins. The features such as these together with imbricate faults, listric faults and decollement are also described  in detail elsewhere in this assembly.