COMPRESSED STRUCTURE IN WESTERN INDIANA. 4929 
NOTE ON AN AREA OF COMPRESSED STRUCTURE IN WESTERN INDIANA 
BY GEORGE H. ASHLEY 
During the past summer, while engaged in a survey of the coal-fields of Indiana, 
it was the writer’s privilege to find a small area in which the structure showed 
evidences of compression most clearly and unmistakably. The fact is of interesl 
in view of the general rule which holds in the Illinois basin, that all structurat 
irregularities are of the tension order. The abundant faults* are normal faults. 
Joints in the coal or rock are perpendicular and regular. Where pressure seems to 
have been at work it is usually found when traced down to be due to a lateral 
component of a vertical pressure due to load, the action taking place as a result of 
differential shrinkage of the coal-beds. Thus it is usual where a V-shaped chan- 
nel has been cut well down into the coal and filled with sandstone to find the 
coal on either side of such a channel filling thickened and bearing internal evi- 
dence of compression. In such cases, however, the cause is purely local and due 
primarily to the difference in compressibility of the coal and sandstone acting to 
throw a disproportionate load on the sandstone, which, then acting as a wedge, 
simply squeezes out the coal from under itself or-forces it down into the underly- 
ing clay, if that be soft. 
Figure 1.—Reversed Fault, Columbia No. 4 Mine. 
Showing data observed in entry and small test shaft and its interpretation. 
In the case to be described, however, the area affected covers several square 
miles and must be recognized as due to distinctly different causes. This area is in 
Clay county, and lies south and southwest of the little village of Asherville. 
The compression is first observed in the character of the faults. As stated, over 
the basin in general normal faults are the rule. In this area reversed faults are 
the rule. Figure 1, from a sketch in Columbia No. 4 mine, may serve as a good 
type. In this case the overthrust is from the north, the fault line, as noted in the 
entry, dipped 48° to the north. It is evident here that the compressive force has 
acted with some power, and that no inconsiderable shortening has taken place, 
though how much could not be determined. 
The compression is next evident in thickened and crushed coal-beds. This area 
+ : 
* The idea which has long prevailed that beyond the almost imperceptible westward dip of the 
rocks and a few indistinct folds, the strata of Indiana show no traces of structural irregularities 
has recently been found to have been quite erroneous. Inthe prosecution of the present resurvey 
of the coal area, structural irregularities of every kind have been found abundantly, not alone in 
the mines, but in surfaee exposures along the streams and elsewhere; faults of nearly every 
type, clay veins, sandstone, and coal veins, etcetera, as well as such phenomena as are mentioned 
in the present note. 
