^0 



the lower edge of the coal seam on the opposite side of the 

 fissure, as shown in the accompanying figure. 



HORSEBACK IK MINE NO. 5 



Of 



SfMNtlfltU) COAL MlNl.NO Ca 





— GRAY SOAPSTONt 



Black smale 



COAL MO. S 



In this area the fissures have a very limited vertical extent. 

 In the Mechanicsburg mine a coal seam was formerly worked 

 about thirty-five feet above the number 5 bed which is at 

 present being mined.. Although these two coal seams are 

 separated by an interval of less than forty feet, the number 5 

 coal is traversed by numerous clay seams, while none were 

 encountered in the upper bed. 



It seems certain that there was a somewhat ready yielding 

 of the coal mass in a lateral direction when the fissures were 

 formed. This is shown in the fact that the walls of the fissure 

 arc much wider ai)art in the coal bed than in the overlying roof 

 shale and cap rock. The clay seams always cut the bed in an 

 oblique or a vertical direction, never following the partings or 

 stratification planes of the coal scam, even wlicre tliese are well 

 marked, 'line amount of downward slipping of the cap rock 

 is always less than the extent to which the u])per edge of the 

 coal scam overhanging the fissure is bent downward. .Ml of 



