148 



KANSAS UNIVERSnV QUARTERLY, 



of one side corresponding closely to those on the other implying 

 that the coal had been broken asunder and separated horizontally, 

 while in rare cases a vertical displacement of a few inches or a 

 foot has taken place. Frequentl}' angular fragments of coal have 

 lodged in the clay filling as though it had dropped from the roof 

 wall during the process of filling. 



The horizontal position of the coal or shale strata usually has 

 not been disturbed, but in some cases the strata adjacent to the 

 fissure have been lifted up as though after the fissure was formed 

 and filled with the clay a lateral compression occurred with a 

 slight bulging upwards of the ends of the strata in contact as 

 represented in Fig. 2. 



Extent and FkEguENCY of the Fissures. - The extent of the 

 fissures, both vertically and laterally, can hardl}' be determined. 

 The processes of mining operations are confined to so small a dis- 

 tance vertically that the fissures cannot be studied below tlie coal to 

 any considerable extent, and the tunnels and driveways are made in 

 such a way and tht- mines located in such positions that it is also very 

 <lifficult, or in fact impossible, to find the lateral extent of many of 

 the fissures. It is known that some of them extend continuously 

 for half a mile or more, but beyond this it is largely guess work, 

 althougli it is ju-obablc that manv of tliem e.xttiul much farther. 



I<'ig. 4. — Horseback sbowiiij; displai-ement of o:)al and shiilo. imd fracturo of c )al. 



Contents ok the Fissures. — The contents of the fissures consist 

 in most cases of fire clay which has doubtless been produced by 



