I9I3.I STEVENSON— FORMATION OF COAL BEDS. 115 



the foreign material tapers downward as if introduced from above. 

 Often there is no serious distortion, and the coal shows only such 

 irregularity in structure and com])osilion as might be expected if the 

 process of accunudation was more or less interrupted. The varia- 

 tion in the coal is usually such as to indicate that the *' trouble " had 

 its origin, at the latest, before the coal was consolidated ; but this 

 is not always the case. At the same time, one must not fail to 

 recognize that many times there are disturbances in the immediate 

 proximity, which appear to be directly related to the " washout " ; 

 irregular cracks and faultings frecjuently occur, and the cracks are 

 filled with clay from the partings or even from the " washout " stuff 

 itself. These conditions are due to disturbances of later date; the 

 effect of the force, which caused the gentle folding of the strata, 

 became especially distinct where the mass of resistant rock had been 

 thrust into the brittle coal. 



Blandy^-^ has described the conditions observed in the Red Bank 

 Mining property in Armstrong county of Pennsylvania. The work 

 of removing the coal from these miines had been made unprofitable 

 by "horsebacks," as the miners termed the rolls of indurated clay 

 descending from the roof. These seldom reached the floor but very 

 frequently and for considerable distances, replaced all but 3 or 4 

 inches of the coal. It was necessary to ascertain the extent of these 

 troubles before reaching a decision respecting farther continuance 

 of operations. Blandy's systematic survey yielded the results pre- 

 sented on the map, which accompanies his paper. These " troubles " 

 mark ancient water-courses. The chief stream was followed for 

 about 1,700 feet and several well-defined branches were mapped. 

 At the southerly end of the workings, another stream was encoun- 

 tered, nearly 100 feet eastward from the former. These stream- 

 courses diverge northwardly, so that at the boundary of the property 

 they are 1,200 feet apart. In another mine, somewhat farther east, 

 the course of a third stream was followed for more than 600 feet, 

 its branches being traced to varying distances. This stream curved 



^^J. F. Blandy, "On Evidence of Streams During the Deposition of the 

 Coal," Trans. Amer. Inst. Mining Engrs., Vol. IV., 1875, pp. 113-116. 



