axis, as at the Shenandoah City Colliery. The upper part of the slope is there sunk through rock (a "Rock-slope") and should therefore be called an incline* rather than a slope, but this distinction is not recognized by the miners.

A tunnel opening is sometimes made when the coal, dipping steeply in the same direction as the slope of the hillside, outcrops on an adjoining property; or when it turns over forming a saddle in the hill.

Nearly all the early mining operations were prosecuted through water-level openings, -drifts and tunnels,-driven in from the surface and giving access only to the coal lying above water-level. The amount of coal now accessible in this way is comparatively small, for these old workings exhausted or ruined portions of the best and thickest coals lying above water-level.

Slopes are greatly preferred to shaft openings at all points in the anthracite regions where the coal is accessible along its outcrop and where the dip is more than 15° or 20°.

The usual practice is to sink the slope and its air-way side by side, and at a depth of from one hundred to one hundred and ten yards on the bed to open out a "lift" by driving gangways to the right and left. The breasts opened along these two gangways (east and west) constitute the "First Lift." This is often worked for several years before the slope is sunk to open a second lift, but it is now frequently the practice to continue the sinking without waiting until the coal on the upper level is nearly exhausted. When this is done, work on the slope is prosecuted at night,—at least the raising of rock and coal and lowering of supplies,—so that this work does not interfere with mining and raising coal from the upper level.

The "Second Lift" is usually opened out at a depth of from seventy-five to one hundred yards from the first lift.

Sometimes three or four lifts are open at once, but there are few collieries mining coal from more than three lifts at the same time.

In "lift" mining the water is pumped from each of the

*See Glossary.

different gangways, and at many collieries nearly all the water is caught on the first and second lifts; the lower levels being very dry. The surface water is often caught on the water-level gangway or drift, driven between the outcrop and the first lift, and conveyed directly from the mine without pumping.

When the coal is to be opened by shaft, it is generally considered best to locate the main opening directly over the deepest part of the basin found on the tract to be developed.

Before the best location can be intelligently determined it is absolutely necessary to have all the geological information attainable represented on an accurate map, and one or two cross-sections constructed to show the geological structure. The depth of the basin and its location as shown by these sections, may or may not be trustworthy, and in my opinion, it is therefore never wise to proceed until the results so obtained have been verified by a series of bore holes, especially if the proposed opening is in a district subject to marked irregularities in the condition of its coal seams. The proper location of the main winding and pumping shaft, for the most economical extraction of the coal is a matter of such vital importance that the expenditure of a few thousand dollars in preliminary exploration by boring seems by comparison a small matter.

The Pennsylvation Mines Ventilation Act requires two openings not less than one hundred and fifty feet apart. Unless the coal to be worked lies in two sub-basins, the location of the second outlet is not a matter of much importance; but if the tract to be developed is crossed by more than one axis, the second opening is best located in the trough of the minor basin, and may then be used for raising coal and water from the area that cannot be economically worked from the first shaft. Other things being equal, it is evident that it is advisable to have the two openings some distance apart.

The coal of the future will be raised from deep mines, through shafts, and as shaft after shaft is sunk in progressively deeper portions of our anthracite basins, this subject -the proper location of shafts-will be more generally

recognized as one of preeminent importance. In the Pottsville, Wyoming, Ellengowan, etc., basins, the great masses of untouched coal lie at considerable depth, and can only be worked through shaft openings.

When a shaft passes through two or more workable beds, the mining operations then closely simulate "lift mining," and in such cases nearly all the water is usually caught in the upper beds; thus at the large Pottsville shaft the water is nearly all caught in workings on an upper bed at a depth of about three hundred feet.

CHAPTER IV.

Shaft sinking and timbering.

Winding shafts in the anthracite mining regions are always square or rectangular; second openings used as upcast airways are occasionally round.

The surface material-earth, clay, gravel, or loose sandpassed through before reaching bed-rock is usually not more than twenty feet thick, and for this thickness an ordinary cribbing of heavy timbers (12X12 or 12X16) or a masonry curbing is generally sufficient; but when the surface material is much thicker, or when the material is loose and runs like quicksand, or is water-logged, a double curbing is necessary.

Under such conditions the shaft is often at once divided into the required number of compartments by heavy bun tons alternating or placed "skin to skin," thus effectually bracing the cribbing against the lateral pressure exerted by loose material.

In the Wyoming Valley at points where a large amount of diluvial material must be passed through before reaching bed-rock, much difficulty will be experienced in the future

in attempting to sink shafts to develop the deeper portions of the basin between Pittston and Nanticoke.

The deposits of clay, gravel, and sand now filling the old valley of the Susquehanna river between these points, is in place one hundred and fifty feet deep. To sink through such a mass of loose material we will probably be forced to avail ourselves of the methods now used in several of the European coal fields.

The English and French works are filled with descriptions of water-tight tubbing, moss-boxes, etc., that have been successfully used in sinking through loose and water-logged strata. It is not within the province of this report to discuss the relative merits of the different systems in use abroad, but it does not seem probable that any of these methods will be entirely successful in the anthracite regions. They will doubtless be modified to meet the peculiar conditions of each case-but these modifications must in some respects be radical, and the best results will probably be obtained by adopting, from each of the several systems, the methods and appliances that have given the best and cheapest results.

Size of Shafts.

The average size of shafts now being opened in the anthracite regions is considerably larger than in former years. This change has resulted from three causes.

1. Greater depth of shafts to open undeveloped coal in the deeper portions of the main basins, which necessitates 2. Larger cross-section, to secure better ventilation for these more gaseous mines.

3. The policy now adopted of opening one large colliery in preference to two small mines, necessitating better hoisting facilities.

The width of shafts is usually governed by the length of the mine cars, which ranges from 9 to 10 feet; hence, the width adopted is usually 10, 11, or 12 feet.

The length is governed by the number of compartments, and by the area of airway needed.

The compartments are now made from 6 to 8 feet broad, inside the buntons, or an average of about 63 feet between

the guides; hence, the compartment, measured between the centers of the buntons, is usually from 7 to 9 feet.

The length, therefore, varies from 16 to 20 feet, for a shaft with two compartments, 30 to 38 feet for a shaft with four compartments (22 to 26 feet being the ordinary length for three compartments,) to 44 to 52 feet for a shaft with six compartments.

When this large number of compartments (6) is provided, two are usually used for an upcast airway, as at the Exeter shaft, (see Atlas, Plate II,) and for the pump-rods and column-pipe, and in some cases one is used with the hoisting compartments as a downcast, while at other shafts two extra hoisting compartments are held in reserve for future requirements, as at the Exeter colliery.

The shafts at present operated in the anthracite region are very rarely more than eight hundred feet deep; their average depth is probably between three and four hundred feet.

The deepest shafts are found in the neighborhood of Wilkes-Barre, and in the southern basin, near Pottsville, where shafts from six to eight hundred feet deep are not

uncommon.

The dimensions and depth of some shafts in the WilkesBarre district are given in the following table.