In displacements of this class the principal direction of movement is horizontal, and in horizontal strata may readily escape detection. When the strata are inclined, a horizontal displacement produces effects which in cross-section cannot be distinguished from those of ordinary normal and reversed faults, except when the striae of slicken-sides remain to indicate the actual direction of movement. The deceptive appearance is exactly the counterpart of that which results from the vertical movement of a dip-fault, by which the offset of the outcrop is brought about. This is illustrated by the model, Figs. 179, 180, which shows that if the hanging wall is moved in a direction opposite to that of the dip of the beds, an apparently normal fault results, while if it is moved in the same direction as the dip, an apparently reversed fault is produced. Horizontal faults do not form scarps, for there is no vertical movement, but in certain cases, as shown by the striae, the movement is obliquely upward. It is thus evident that what would ordinarily be regarded as normal and reversed faults of the typical kind may readily be formed by the same movement.

For a long time these heave-faults were supposed to be very rare, but they are now known to be quite common, and doubtless very many faults, which have been regarded as normal or reversed, will on further study turn out to be heaves.