It is here seen that the grooves are at right angles with each other, and the block of stone is sheared by a break made opposite and parallel with the bench, as in the previous case, and an additional break made at right angles with the bench and at the fixed end of the block.  Sometimes a corner break is made by putting in two of the regular V-shaped holes in the lines of the proposed break and without the use of the corner hole.  A useful application of this system is in splitting up large masses of loose stone.  For this purpose the V-shaped grooves are sometimes cut in four positions and breaks are made in four directions radiating from the center of the hole as shown in Fig. 12.  In this way a block is divided into four rectangular pieces.

[Illustration:  FIG. 12.]

Though the new system is especially adapted to the removal of heavy masses of rock, yet it has been applied with success in cases where several light beds overlie each other.  In one such instance 10 sheets, measuring in all only 6 ft., were broken by a blast, but in cases of this kind the plug and feather process applies very well, and the new system, when used, must be in the hands of an expert, or the loss will be serious.

Referring again to our stone step, let us imagine a case where this stairway runs between two walls.  We have here each step fixed at each end and free only on the top, the bottom, and one face.  Let us assume that there is a back seam, that is, that the step is not fixed at the back.  In a quarry, this seam, unless a natural one, should be made by a channeling machine.  In order to throw this step put of place it must be cut off at both ends, and for this purpose the V-shaped holes are put in at right angles to the face.  It is well, however, to put the first two holes next the back seam in a position where the grooves will converge at the back so as to form a sort of key, which serves a useful purpose in removing the block after the blast.  In quarries where there are no horizontal beds a channeling machine should be used to free the block on all sides and to a suitable depth, and then the ledge may be “lofted” by holes placed horizontally.

Where “pressure” exists in quarries, the new system has certain limitations.  After determining the line of “pressure” it is only practicable to use the system directly on the line of thrust, or at right angles to it.  It is much better, however, to release the “pressure” from the ledge by channeling, after which a single end may be detached by a Knox blast.  It is well to bear in mind that the holes should invariably be of small diameter.  In no case should the diameter of a hole be over 11/2 in. in any kind of rock.  This being the case, the blocks of stone are delivered to the market with but little loss in measurement.  It is a noticeable fact that stone quarried by the new system shows very little evidence of drill marks, for the faces are frequently as true as though cut with a machine.