1871.] 85 [Mies. 



In three instances,. I have Lad the opportunity of observing the 

 rock, when it has been split at shorter lengths in the manner de- 

 scribed above. In each case the expansion was sufficient to admit 

 of measurement. 



Near the upper end of the quarry, four hundred holes had been 

 drilled into a bed, making a row one hundred and twenty-eight feet 

 long. When the wedges had been driven sufficiently to merely frac- 

 ture the rock, and while most of them were still firmly held, the ex- 

 pansion amounted to one-sixteenth of an inch. The stone which had 

 so expanded, was eleven feet wide, and three feet thick at the lower 

 end, and five feet thick at the upper. In this example the upper 

 end was the one attached, and the extension was southward. 



Near the southern end of the quarry, a split thirty- three feet and a 

 half long had been made. Here the slab was firmly attached to the 

 bed at the lower end. Its width was six feet and nine inches, and its 

 thickness one foot and eight inches. I was permitted to take out 

 the wedges, when I found the expansion amounted to one eighth of 

 inch at the upper end. I could distinctly see that it increased reg- 

 ularly in amount, from the lower end to the upper. 



The other instance was in the working of a bed, the western edge 

 of which extended in a direct line along the strike, without having 

 been anywhere cut or fractured transversely. A row of wedges fifty- 

 eight feet long was driven into holes upon the upper surface of the 

 bed, and seven feet from its edge, thereby splitting the bed only 

 along the line of the wedges. It was then necessary to cut from the 

 western edge of the bed eastward to this fracture. The workmen 

 attempted to do this by taking out a piece in the form of a triangle, 

 the base of which was upon ' the edge of the bed, and the apex 

 reached the upper end of the fracture. They found this a somewhat 

 difficult task. The piece appeared to be held by something more 

 than the tenacity of the rock, and it was necessary to break it into 

 small pieces before it could be removed. When considerable stone 

 had been cut away, cracking sounds were heard, and the remaining 

 portion of the triangular mass was quickly fractured and easily re- 

 moved. For two hours I had been watching the corresponding halves 

 of the drill holes, at the upper end of the fracture first made by the 

 wedges, to observe at what period of the work, the expansion, if 

 any, should take place. The halves of the holes remained perfectly 

 conformable in position, up to the time of the cracking sounds and 

 the loosening of the stone, but immediately upon this taking place, 



