Transverse sections, such as are represented by Fig. 28 and many specimens and models, do not give the complete plan or idea of a fault; but this is seen more perfectly in Fig. 30. We learn from this that a typical fault is a fracture along which the strata have _sagged_ or settled down unequally. The most important point to be observed here is that the strata do not drop bodily, but are merely bent, the throw being greatest at the middle of the fault and gradually diminishing toward the ends. In other words, every simple fault must die out gradually; for we cannot conceive of a fault as ending abruptly, except where it turns upon itself so as to completely enclose a block of the strata, which may drop down bodily; but the fault is then really endless. A fault may be represented on a map by a line; if a simple fault, by a single straight line. But faults are often compound, and are represented by branching lines; that is, the earth’s crust has been broken irregularly, and the parts adjoining the fracture have sagged or risen unequally. [Illustration: Fig. 30.—Ideal view of a complete fault.] The rock above an inclined fault, vein, or dike (Fig. 28) is called the _hanging wall_, and that below the _foot wall_. Now inclined faults are divided into two classes, according to the relative movements of the two walls. Usually, the hanging wall slips down and the foot wall slips up, as in Fig. 28. Faults on this plan are so nearly the universal rule that they are called _normal_ faults. They indicate that the strata were in a state of tension, for their broken ends are pulled apart horizontally, so that a vertical line may cross the plane of a stratum without touching it. A few important faults have been observed, however, in which the foot-wall[**no hyphen before] has fallen and the hanging-wall[**] has risen (Fig. 29). These are known as _reversed_ faults; and they indicate that the strata were in a state of lateral compression, the broken ends of the beds having been pushed horizontally past each other, so that a vertical line or shaft may intersect the same bed twice, as has been actually demonstrated in the case of some beds of coal. [Illustration: Fig. 31.—Explanation of normal faults.]