812 J. F. NEW SO M 



and it is probable that the escaping gas was ignited by this 

 fire. 



The accompanying figures show the nature of the fissures that 

 were produced by the explosion. 



Catise of the explosion. — The explosion was supposed at the 

 time to have been caused by gas escaping below the casing from 

 the wells at either St. Paul or Waldron, or at both places, and 

 finding its way between the strata to the point where the explo- 

 sion took place, at which point the strata were too weak to 

 withstand the pressure. 



Whether the gas did come from these wells, whether it came 

 up from below through a crevice, or whether it was generated 

 at no great depth in the strata, more or less directly below the 

 area where the explosion occurred, is not known. 



It is evident, however, that gas accumulated below an 

 impervious layer until the pressure became sufficient to rend this 

 impervious bed, when the explosion followed. The pressure 

 required to do this cannot be known, because neither the depth 

 nor strength of the confining strata is known. 



It is obvious that gas, under a pressure of say two or three 

 hundred pounds to the square inch, if confined by horizontal 

 strata, sufficiently near the surface so that the weight of the 

 overlying material would not equal the pressure of the gas, 

 would tend to spread laterally between the strata, and to cause 

 these to bend upwards. If the pressure should become great 

 enough, the strata would finally break and the gas would escape, 

 possibly with explosive violence. Such an explosion would not 

 necessarily indicate that a large supply of gas was involved, for 

 a small quantity would exert as great a pressure to the square 

 foot as a larger one. 



The area affected by the Ogden Cemetery explosion covered 

 about ten acres ; the pressure on this surface at 250 pounds 1 per 

 square inch would have been 36,000 pounds to each square foot 

 of surface. 



Taking the weight of the shales and surface soil as 175 



1 The "rock pressure" of the gas in some portions of the Indiana field in 1890 

 was over 300 pounds to the square inch. 



