DISRUPTION OF ROCK BY LIGHTNING 569 



kind. The nearest trail is in Long Canon, one mile northwest and 

 four hundred feet lower down. Over this trail there is perhaps not 

 more than one person a week during summer and probably fewer in 

 winter. Several coal prospects have been opened, however, during 

 the last five or six years, in Back Canon and also in Long Canon, not 

 more than five miles to the south, but giant powder only was used in 

 shooting. Had a prospector been so disposed it is the writer's opinion 

 he could not have produced the effect shown in this photograph with 



Fig. I. — View on top of Cross Mesa, Wyoming, showing fragments torn from 

 the lava by lightning. 



ordinary blasting powder. He certainly could not have done it with- 

 out a drill hole and no evidence of holes were observed. Even with a 

 drill hole it would have been very hard, if not impossible, to have 

 confined the powder sufficiently well. Furthermore, from the very 

 nature of the rock (lava), a prospector would not have been looking 

 for minerals in this place, and if he had been doing it for amusement 

 he almost certainly would have selected a crevice at the limiting cliff 

 of the mesa where the explosion would have loosened a large mass of 



