In 1872 a slip occurred for forty miles on the great line of dislocation which runs along the eastern base of the Sierra Nevada Mountains.  In the Owens valley, California, the throw amounted to twenty-five feet in places, with a horizontal movement along the fault line of as much as eighteen feet.  Both this slip and that in Japan just mentioned caused severe earthquakes.

For the sake of clearness we have described oscillations, foldings, and fractures of the crust as separate processes, each giving rise to its own peculiar surface features, but in nature earth movements are by no means so simple,—­they are often implicated with one another:  folds pass into faults; in a deformed region certain rocks have bent, while others under the same strain, but under different conditions of plasticity and load, have broken; folded mountains have been worn to their roots, and the peneplains to which they have been denuded have been upwarped to mountain height and afterwards dissected,—­as in the case of the Alleghany ridges, the southern Carpathians, and other ranges, —­or, as in the case of the Sierra Nevada Mountains, have been broken and uplifted as mountains of fracture.

Draw the following diagrams, being careful to show the direction in which the faulted blocks have moved, by the position of the two parts of some well-defined layer of limestone, sandstone, or shale, which occurs on each side of the fault plane, as in Figure 184.

1.  A normal fault with a hade of 15 degrees, the original fault scarp remaining.

2.  A normal fault with a hade of 50 degrees, the original fault scarp worn away, showing cliffs caused by harder strata on the downthrow side.

3.  A thrust fault with a hade of 30 degrees, showing cliffs due to harder strata outcropping on the downthrow.

4.  A thrust fault with a hade of 80 degrees, with surface baseleveled.

5.  In a region of normal faults a coal mine is being worked along the seam of coal ab (Fig. 193).  At B it is found broken by a fault f which hades toward A. To find the seam again, should you advise tunneling up or down from B?

6.  In a vertical shaft of a coal mine the same bed of coal is pierced twice at different levels because of a fault.  Draw a diagram to show whether the fault is normal or a thrust.

7.  Copy the diagram in Figure 194, showing how the two ridges may be accounted for by a single resistant stratum dislocated by a fault.  Is the fault a strike fault, i.e. one running parallel with the strike of the strata, or a dip fault, one running parallel with the direction of the dip?

8.  Draw a diagram of the block in Figure 195 as it would appear if dislocated along the plane efg by a normal fault whose throw equals one fourth the height of the block.  Is the fault a strike or a dip fault?  Draw a second diagram showing the same block after denudation has worn it down below the center of the upthrown side.  Note that the outcrop of the coal seam is now deceptively repeated.  This exercise may be done in blocks of wood instead of drawings.