“R46 
in the entry. A possible cause of faults of the last two types is thought to 
be the uneaual subsidence of underlying basins of coals. In a basin 
where, as is usually the rule, the coal is quite thick in the center and very 
thin on the edges, the actual shrinkage is much greater in the center of the 
basin than on the edges. A certain percentage of this shrinkage is known 
to take place after the deposition of the overlying beds. Where a channel 
has been cut in the coal and filled with sandstone an irregular belt results 
which resists compression much more than the coal adjacent and might 
lead to a fracturing of the overlying strata, as the subsequent unequal 
settling takes place. This is suggested merely as one possible cause of 
such faults. These faults are very irregular as regard course and direc- 
tion of down-throw, frequently crossing each other, sometimes being very 
short and again traceable in two or more adjacent mines. In the Dugger 
Mine, Sullivan County, three faults cross each other in the same vertical 
line at one place. 
Considering the structure of the faults at the fault line, itis found that 
frequently the fault line appears sharp and clear cut, as in most of tne 
figures of plate I, and it is only on very close examination that any 
crushing can be detected. In other cases, however, the crushing effect has 
been intense for several feet, or even several yards, on either side of the 
fault line. This often occurs where the down-throw is hardly noticeable. 
At such a fault there is very apt to result an intrusion of clay or other 
material, making clay veins, sandstone veins, etc. Figures 3 to 9 of plate 
II illustrate this. The way the pressure has forced the clay out in irregu- 
lar streamers, as in figures 3 and 4,or simply forced it into the coal in irreg- 
ular masses, as in figure 5, give some idea of how completely pulverized the 
’ 
adjacent coal often is. ‘Lhe sandstone veins, or “rock spars,” as they are 
usually called in the mines, are generally very hard sandstone. Appar- 
ently they are somewhat similar in origin with the clay veins, though we 
are not entirely satisfied that such is the case. In figure 14 a surface 
crevice has had coal washed in, making a coal vein of a certain type. 
If such a crevice be considered as probably resulting from fault action 
in the neighborhood it would indicate that some of the faulting took place 
during the laying down of the-coal measure rocks. This vein occurs about 
ten feet below the lowest worked coal in Indiana. 
Overthrust faults and accompanying phenomena are not Common, as 
compared with normal faults. They are met with in various parts of the 
field, but the amount of accompanying crushing often renders the structure 
