: 
245 
mining or good bluff exposures give an opportunity to observe them, that 
Indiana contains thousands of faults of appreciable down-throw. In some 
districts there is hardly a mine that does not contain from one or two to 
several dozen. 
In their relation to the general structure the normal faults divide 
themselves into four classes, as typified in figures 1 to 4, plate I. In the 
first type, which might be called the monochinal fault, the fault is simply 
a fractured monocline, the down-throw of the fault usually not being as 
great as the differences of level above and below the monocline. Such a 
fault may consist of a single break or of two or more breaks, known as 
a step fault. In some cases the same fault will show as a single break at 
one point and as a step fault at another point, as in the case illustrated by 
figures 6 to 8 of plate I. Figures 5, 9 and 10 further illustrate the same 
type of fault. : 
In the second type of fault the hade is in the opposite direction from 
the general dip. Figures 11 to 13 of plate I illustrate this type of fault. 
Such a fault usually occurs as a series of breaks, resembling a broken 
arch, a type of fault common in the western part of the United States. 
Faults of the two types mentioned constitute a class that appears 
to be due to the uneven settling of the Illinois basin area. These faults, 
taken as a whole, do not appear to have any uniformity in the direction 
of down-throw or of strike... However, if only the larger faults be consid- 
ered, a majority of them trend between northeast and northwest and have 
the down-throw to the west. There are so many notable exceptions that 
it can not be considered as a rule. Thus, in Martin County, from Shoals 
westward, the dip is nearly everywhere observed to be strongly to the 
west, yet so many faults with the down-throw to the east occur in that 
region that the strata are higher five miles west of Shoals than at Shoals. 
In the third and fourth types the faults appear to be due to quite local 
causes, as the strata a short distance on either side are on about the 
same level. Figure 14 of plate I and figure 2 of plate II illustrate the two 
types, respectively. The difference between the faults of the first two 
types and those of the last two are very well shown in the effect on the 
driving sof entries in the mines. Thus, a six-foot fault of the first type 
necessitates driving the entry up or down until it is at least six feet 
above or below its old level, according as the fault is approached. A. six- 
foot fault of the third type can be passed with little or no change of level 
