ry run smoothly.]

An "oil field" may extend over thousands of square miles; but within
this field there are always "pools"; that is, certain smaller fields,
where oil is found. When a man thinks there is oil in a certain spot,
sometimes he buys the land if he is able; but oftener he gets
permission of the owner to bore a well, agreeing to pay him a royalty;
that is, a certain percentage of all the oil that is produced. When
this has been arranged, he builds his derrick. This consists of four
strong upright beams firmly held together by crossbeams. It stands
directly over the place where the well is to be dug. It is from thirty
to eighty feet in height, according to the depth at which it is hoped
to find oil. There must also be an engine house to provide the power
for drilling. An iron pipe eight or ten inches in diameter is driven
down through the soil until it comes to rock. Now the regular drilling
begins. At the top of the derrick is a pulley. Over the pulley passes
a stout rope to which the heavy drilling tools--the "string of tools,"
as they are called--are fastened. The drilling goes on day and night.
The drill makes the hole, and the sand pump sucks out the water and
loose bits of stone. When the drill has gone to the bottom of the
strata which carry water, the sides of the bore are cased to keep the
water out; then the drilling continues, but now the drill makes its
way into the oil-bearing sandstone.

There is nothing certain about the search for oil. In some places it
is near the surface, in others it is perhaps three or four thousand
feet down. The well may prove to be a gusher and pour out hundreds of
thousands of gallons a day; or the oil may refuse to rise to the
surface and have to be pumped out even at the first. Naturally, no one
is prepared for a gusher, and millions of gallons have often flowed
away before any arrangements could be made for storing the oil.
Sometimes a well that gives only a moderate flow can be made to yield
generously by exploding a heavy charge of dynamite at the bottom, to
break up the rock and, it is always hoped, to open some new
oil-holding crevice that the drill has not reached.

Crude petroleum is a dark, disagreeable, bad-smelling liquid; and
before it can be of much use, it must be refined. For several years it
was carried in barrels from the oil fields to Pittsburgh by wagon and
boat, a slow, expensive process, and generally unsatisfactory to all
but the teamsters. The