the walking-beam thrown up out of the way. The tools are then run up, but are stopped when the bit reaches the level of the derrick floor, where it is loosened by large wrenches, 3' long; the tools are then run up clear of the hole, the bull-rope thrown off, the brake applied, and steam shut off. The tools are drawn aside and held by a hook, and the bit removed and replaced by one newly dressed. While this is being done, the sand-pump is run up and down once or twice, by means of the friction-gear and brakeblock, already described.

After cleaning out the sediment in this way, the tools are again swung over the hole and the bit tightened up. The tools are then run down-controlled by the bull-wheel brake the walking-beam connections made, the temperscrew clamped to the rope, and another "run" is commenced.

The average cost of drilling a well in the oil country in 1878 was as follows:

"Rig," complete,

Belt, bull-rope, telegraph, water pipes, and steam fittings,

Boiler (20 H. P.) and engine (15 H. P.,) on ground, Contract for drilling, drillers to furnish fuel, tools, cable, sand-pump, and line, &c., @ 65c. a foot, 1500 feet,

$350

100

750

975

$2,175

As prices were at their lowest ebb in 1878, this estimate should probably be increased by about 20%; say to $2,500, to make it available for comparison with other methods at the present time [1882.]

The average rate of drilling, in the Butler county oil

field, where the rocks are much harder than in the McKean district, ranges from twenty-five to fifty feet a day (twentyfour hours); but sometimes as much as a hundred feet is drilled in one day, under favorable circumstances, while a very hard "shell" one or two feet thick may require twenty-four hours of hard work.

The cost of drilling prospecting holes by this method in the anthracite regions will be very much greater than that shown by the above figures, because the rocks are much harder, and are inclined at considerable angles from the horizontal.

The high inclination of the rocks increases the risk of flat and crooked holes, and necessitates careful watching and constant and uniform rotation of the drill. In some districts, as, for instance, the Wyoming basin, the hardness of the rocks is not a serious obstacle, but will probably reduce the average drilling speed to less than one half that attained in the oil regions. This will add materially to the cost. We have not sufficient data on which to base general conclusions as to the cost per foot of rope drilled holes, but it certainly seems probable that they can generally be sunk much cheaper (for deep holes) than by the diamond drill process.

This process (rope drilling) has also been used for drilling holes for steam and compressed air pipe, for pump-holes to replace column pipe, for artesian wells, (as is being done at present at Nesquehoning Tunnel,) and for holes used as ropeways, for conducting an inside slope rope to a winding engine at the surface. A hole 600 feet deep has lately been drilled for this purpose by the Lehigh and Wilkes-Barre Coal Company at the Hollenback Colliery.

Percussion Power Drills.

Although for limited depths percussion drilling machines may be used for prospecting, the principle on which they are constructed disqualifies them from the work of deep boring. They have not sufficient drawback power to lift a long line of rods in a vertical hole, and in a horizontal hole the impact of long rods is ruinous to the machinery. About

the only prospecting that can be economically done with them, is the drilling of holes of limited length into unknown ground from the galleries of a mine already opened.

The Diamond Drill.

This drill has been largely used for prospecting purposes in the anthracite regions, and generally with good results. The claim frequently made that complete cores can be obtained showing the exact condition of a coal bed, cannot be entirely substantiated, for the cores so obtained are not infrequently very imperfect and are often little if at all better than loose fragments, and at times a considerable portion of the core is completely pulverized and lost.

It is also claimed that the cores show the dip of the rocks, but as the rocks may be false-bedded or may exhibit a decided cleavage not coinciding with the bedding, it is not safe to base any important conclusions on deductions based alone on the apparent dip shown by the cores.

The cost of drilling deep holes with the diamond drill in rocks of moderate hardness is certainly much greater than by the rope-drilling method as practiced in the oil regions, and the progress made is also much slower,-the cores obtained may or may not be worth the difference in time and money.

When a large number of comparatively shallow holes are to be drilled in hard rocks; or prospecting holes are needed from some point inside a mine; or when inclined or horizontal holes are required, the diamond drill will give the best results.

The "long-hole" method of shaft sinking by the diamond drill will be considered in another chapter.

This drill is so will known among mining men, and it has been so thoroughly illustrated and described in various publications, and by circulars issued by the company, that it has not been considered necessary to illustrate it by engravings or to dilate upon the details of its construction and operation. When a large number of holes of moderate depth are drilled by a corporation owning and operating the drill, the cost per foot may, by proper management, be much re

duced. Mr. Lewis A. Riley* reports the average cost of 24 bore holes (ranging from 100 to 900 feet in depth) aggregating 9902 feet, at $2.22 per foot. Their average depth was about 400 feet. The average progress made in ten hours was 18.9 feet. The above estimate of $2.22 per foot covers everything except royalty, interest on investment and wear and tear, for which 20 or 30 cents should be added.

For holes double this average depth of 400 feet the cost per foot would probably be nearly if not quite doubled. Mr. Riley divides the cost thus:

In the transactions of the American Institute of Mining Engineers, Vol. II, page 241+, Mr. Oswald J. Heinrich gives figures that show how rapidly the cost of drilling by this method increases with the depth. The boring was done at the Midlothian collieries in Virginia.

His estimates were based on the following scale of wages

Constructing Geological Cross-Sections.

The practical value of data obtained from surface examinations, prospecting holes, entries and shafts is greatly enhanced by properly constructed cross-sections and maps,

*Transactions American Institute of Mining Engineers, Vol. V, page 306.

and these are always serviceable in planning future developments.

When all the outcrops with their dips, the prospecting entries or shafts and the bore-holes, have been carefully located on the map an attempt may be made to draw lines connecting the isolated outcrops, to represent the approximate position of the coal blossoms on the surface.

To avoid the possible error of connecting outcrops on two different seams the number and order of the coals is first determined by a comparison of local sections compiled from exposures noted in making the surface examinations.

The course of the outcrop line of any layer in stratified deposits is governed by the dip of the stratum and the contour of the surface. When the dip is vertical the surface contour does not affect the course of the outcrop which is then coincident with the "strike"*; in horizontal seams the outcrop follows every irregularity of the surface, accurately conforming to the curvature of a water-level surface contour line. Between these two extremes of the vertical and horizontal dips, all degrees of gradation, are found so that it is often a rather difficult problem to determine how much an outcrop line will be deflected to one side or the other by surface irregularities.

Probably the most trustworthy plan is to trace the outcrop of some prominent stratum and use its position as a key to the course of other outcrop lines.

When a contoured map of the surface can be obtained the location of the outcrop lines is greatly simplified; but the construction of such a map generally involves more labor than can be expended upon it. A rude sketch con- . tour map can sometimes be made at the same time with the surface examinations, that will be serviceable, even if only approximately correct.

Such a map will show the trend of the hills, which usually nearly coincides with the strike of the rocks, the best route. for a railroad or wagon road, and many other valuable facts may be developed by it, for as topography and geology bear

*"Strike": the direction of a water level driven in the bed.