Hawortu. | Detailed Geology. 95 
good supply not so highly mineralized as that coming from 
Shoal creek and quite suitable for boilers. : 
A much larger amount of water is used for milling purposes 
than for steam boilers. Any kind of mineral water will do 
for this purpose providing it does not corrode metallic parts 
of machinery too extensively. Water which has much free 
sulphuric acid is unsuitable, as it corrodes the metals about 
the mills so extensively that repair bills are greatly increased. 
The ordinary custom is to pump mine water into surface 
reservoirs from which it is drawn for milling purposes. 
When the ground water becomes sufficiently bad, as it often 
does, there is great objection to this source of supply. These 
surface reservoirs have another source of contamination aside 
from the bad water of the mine. They are receiving drains 
constantly from the gravel piles produced by the mills. These 
gravel piles contain traces of zinc blende and iron sulphide 
which are slowly oxidized and the products of oxidation 
leached out and carried directly to the surface pools. It 
frequently happens that surface pools in this way become 
more strongly charged with free sulphuric acid and objection- 
able sulphates than the worst of ground water. 
Second.—Almost all the mines are bothered more or less 
with water which must be pumped out in order that the 
mines may be operated. This water is more abundant in 
some mines than in others, and travels through the ground 
more rapidly in some places than others. In some instances 
one pumping shaft will drain as much as eighty acres, so that 
other pumps are not necessary. In other locations a pump- 
ing shaft will drain only a few acres. This difference of 
drainage is due entirely to the freedom of movement of 
ground water. The Mastin land, southwest of Galena, may 
be cited as an illustration of this. Some years ago Mr. McCann 
had a pumping station on a lease just west of the Mastin land. 
The shaft was sunk to a depth of 165 feet, while most of the 
mining on the Mastin land was conducted at a depth of 85 to 
120 feet. The McCann pumps, although off the Mastin 
ground, kept the water down in a satisfactory manner, leaving 
only such small amounts as the different operators wished to 
pump themselves for their own mills. In the course of time 
