of the vein. If, on the other hand, the vein is found to be strong and regular, possessing well-defined 'fissure characteristics to a depth of 150 to 250 feet, the working vertical shaft might be sunk with comparative safety. No rule can be laid down, however, and the Engineer must always exercise his own judgment.

In the example here given, we have assumed the inclined shaft to be sunk to the same depth as the vertical, for if originally sunk to the first cross-cut, 440 feet (Fig. 196), it would be carried down to the point of intersection and used for ventilation.

The method of surveying and plotting such a mine is simply an application of the principles already explained.

408. The calculation of ore-reserves does not come strictly within the province of the surveyor, yet after completing the survey and plot, he is frequently required to make the calculation. We will therefore consider methods of making it.

In practice the methods employed are various. No general rule can be given, as each expert has a system of his own, and different engineers will not agree, within wide limits, as to the quantity of ore-reserves in the same mine. One may assume as the measure of the ore in sight a rectangular block limited by the outcrop, the depth of the shaft or shafts, and the extreme points of the levels, diminished by the amount extracted. Others, but one-half or one-third of this quantity. The former would be considered an excessive estimate in all cases. The latter too low when the vein possesses great strength and regularity, though even this estimate may be too high, when the conditions are the reverse. The surveyor must exercise his own judgment, exercising caution, however, as the calculation is an important

one.

Assume the development shown in Figs. 194, 195, 196, and let it be required to calculate the ore-reserves when the bounding lines are assumed at the extreme ends of the level drifts, or the

rectangular block ABCD, Fig. 195, and when the average crosssection of the vein is 6 feet, and a cubic foot of the vein matter in place weighs 150 lbs.

Ore stopes, or steps made in mine-workings by and for the extraction of ore, are generally very irregular, the representation here being an ideal one. Suppose the stope-faces to be 11 feet apart and 8 feet high, and that the inclined shaft has extracted 10 × 6 ft. of vein matter, and the levels 7 x 6 ft.

We see that the inclined shaft has exposed the vein for 440+115+115 = 670 ft.; deducting say 15 ft. for inequality of surface, we should have a rectangular block 655 × (400 + 350) ×6 in width = 2947500 cubic feet of ore: to be deducted from this, we have

Stoped out on 1st level east, roughly estimated,

Dividing by 134, the number of cu. ft. required for a ton, and we have 204852 tons of ore in sight.

Another method of calculation is as follows: The longest

drift east is 400 ft. and the shortest 100 ft. Assume the bounding line in this direction to be at a distance east of the shaft,

The longest drift west is 350 ft. and the shortest 100 ft.; take the bounding line in this direction at a distance

or the rectangular block abc F, Fig. 195. Calculate the orereserves, when the other data are the same as before.

This latter method is recommended by competent engineers as the fairest and most reliable for all parties concerned.

409. Fig. 197 shows a longitudinal section, and Fig. 198 a transverse section of a deposit mine with mill connections, the mill to be erected at the point A. From a consideration of the diagram, it is evident that the most convenient method for the transportation of the ore from the mine to the mill would be by a tunnel driven into the mountain, at the end of which is a bin, made in the solid rock and inclined to the tunnel at any convenient angle at which ore will slide into cars; the cars to be run into the tunnel on a track and directly under iron doors which are worked by rack and pinion. The bin is to connect with the ore-chamber by a chute inclined at an angle of 45°, as shown in the diagram.

The lower or mill tunnel should have a slope of 2 inches in 10 feet, so that the loaded cars would descend by the force of gravity, the last car in a train having a brake with which to regulate the speed. The chute should be 12 to 15 feet from the edge of the tunnel, to admit of constructing the inclined bin for the discharge of the ore into the cars. The point in the orechamber, at which it is desired to sink the chute, and the mouth of the lower tunnel being selected, drive a peg to the centre point