** 



Niles.] 84 [January 4, 



heard that they supposed the powder magazine had exploded. On 

 hastening to the spot they found that it was not the powder, but the 

 rock, which had exploded. A portion of a bed of nearly circular 

 outline, and more than thirty feet in diameter and one foot in thick- 

 ness, had been thrown up and broken. When they reached it, a 

 portion at the centre was three feet above the surface from which 

 it was broken, and the rock was still cracking and falling. 



Another very interesting phenomenon is the expansion of the rock, 

 as it is being quarried. 



The most remarkable instance of this was observed in the autumn 

 of 1869. By the use of more than twelve hundred wedges, a bed 

 was split three hundred and fifty-four feet in length, in a line along 

 the strike of the rock. The fracture extended from the northern 

 and upper portion of the quarry southward, for the distance men- 

 tioned, but could be traced no further; so that this slab, w-hich for 

 three hundred and fifty-four feet had been fractured from the rock, 

 was at its lower end, still attached to the bed, apparently as firmly as 

 ever. The stone thus partly loosened, was eleven feet wide and 

 three feet thick. At the upper portion of the fracture it was soon 

 noticed, that the halves of the drill holes upon the freshly broken 

 edge of the slab were not directly opposite their corresponding halves 

 on the edge of the parent rock, but that they had been moved fur- 

 ther up the hill, toward the north. At the extreme lower end, the 

 wedges were still firmly held in the rock, and there was no percepti- 

 ble evidence of any movement. But in passing from the lower end 

 to the upper, the first evidence of expansion was shown in only a 

 slightly oblique position of the corresponding halves of the drill holes. 

 Passing on, the amount of unconformability of position increased 

 regularly, until at the upper end it amounted to an inch and a half. 

 Thus from the lowest wedge to the upper end, the stone was an inch 

 .and a half longer than that portion of the bed from which it had 

 been broken. There is an abundance of testimony to this instance of 

 expansion from those engaged at the quarry, and from those who 

 came to the locality to see the curiosity. The stone was allowed to 

 remain in the position above described for more than two months, 

 and during that time it was exposed to warm and cold, and to wet 

 and dry weather; but these changes of temperature and moisture 

 produced no perceptible difference in the amount of the expansion. 

 As the expansion was from the lower end to the upper, gravity could 

 not have been a cause of the phenomenon. 



