This section is from the book "An Introduction To Geology", by William B. Scott. Also available from Amazon: An Introduction to Geology.
Normal Faults (also called gravity faults) are those in which the fault-plane inclines or hades toward the downthrow side, which forms the hanging wall. "It seems best to use the term normal to cover those faults in which, using the horizontal plane as datum, the hanging wall has dropped relative to the foot." (J. A. Reid.) Locally, at least, a normal fault implies an extension of an arc of the earth's surface, for the beds occupy a greater space, measured across the fault, than they did before faulting occurred. The normal faults may be divided into three groups, as shown in the table.
Fig. 173. - Trough-fault of very small throw. (U. S. G. S).