330 ‘GEOLOGY OF OHIO. 
greater than 100 feet in depth, the horse and gin is often used until coal 
is struck, particularly in mines in which the flow of water is not great. 
It is, however, true economy to erect the permanent hoisting machinery 
of the mine before ground is broken. This has to be done sooner or 
later in any event, and it costs no more to construct it one time than 
another, while the money saved in hoisting rocks and water goes into the 
pocket of the mining adventurer. 
All mines have to be timbered until solid ground is reached. The 
manner of timbering slopes is similar to that of timbering drifts, except 
that the bents require to be set a little closer together. In shafts the 
timbers are laid as tight as possible, and in well regulated mines are 
made of 10-inch square timbers. In some shallow mines in the State 
38-inch plank is: used, but this is mistaken economy. Timbers of 8 inches 
are light enough under any conditions. 
The cost of sinking a slope, 10 feet wide, and 6 feet high, does not 
ordinarily exceed $35 per yard. A shaft 8 feet wide and 16 feet long 
will average in good ground 45 to 50 dollars per yard. This includes 
the expense of timbering, the powder used in blasting, and the raising 
of both rock and water. No uniform rule can, however, be laid down 
in such matters, the nature of the ground, the flow of water, and the 
provisions made in commencing operations for the success of the enter- 
prise determine the expense. Some shafts cost more than double that 
of others under the same conditions, and on the same field the cost of 
sinking varies greatly, the result of the skil] and judgment exercised in 
grading and directing the subterranean excavations. ‘The machinery 
of shaft and slope mines consists of an engine for raising coal, a pump 
for lifting water, and the necessary boiler power. The size of the 
hoisting engine is in proportion to the depth of the shaft and the weight 
of the coal raised. Double engines are coming into use around coal 
mines. ‘Two to four boilers, 36 to 40 feet in length, and of 36 inches 
diameter, are generally needed to procure the necessary steam power 
for lifting coal and water. The drums upon which the shaft ropes 
revolve are 5 to 7 feet in diameter ; the pulley wheels upon the pit head- 
frame of shafts are made 6 or 8 feet in diameter. The hoisting ropes 
are 11 inches in diameter, and are made of iron or steel wire. — 
At many mines where the coal is met within 100 feet of the sur- 
face, less elaborate arrangements suffice, but it is always wisdom to have 
good, strong machinery, and especially to have abundant steam power. 
