166 OIL FIELDS OF TEXAS-LOUISIANA COASTAL PLAIN, [bull. 212. 
Trading Company, which has two steam tank ships of 60,000 barrels 
capacity in the trade regularly. 
The tankage in the field to the middle of 1002 amounted to about 
seven and a half million barrels, of which about four and a half 
million barrels were steel and nearly two million barrels earthen tanks. 
There are a few small wooden tanks scattered throughout the field, but 
these are used mostl}?- as measuring tanks and not to any great extent 
for storage purposes. 
Considerable interest is being taken in the construction of earthen 
tanks in this field, since, if satisfactory, these can be constructed at a 
much less cost than the steel structures. Some of these earthen tanks 
have nothing done to them beyond excaA T ating to the required depth ; 
others are lined with timber, and while some of them are open, others 
are covered with a light board roof. 
The capacity of the steel tanks ranges from 10,000 to 55,000 barrels, 
while the earthen tanks range from 25,000 to 350,000 barrels. 
For fire protection the steel tanks are surrounded by a moat and 
embankment, giving a storage capacity equal to the full content of 
the tank. 
METHODS AND COST OF WELL DRILLING. 
ROTARY METHOD. 
The rotary inothod of drilling is the one used almost exclusively in 
the Gulf Coastal Plain oil fields. This appears to be a modification 
of the Fauvelle system, invented in 1845, and used for some time in 
several of the European oil fields. It is unquestionably the most 
rapid and economical method where the formations to be penetrated 
are for the most part unconsolidated. The vast amount of drilling 
done in this field since the spring of 1901 and the keen competition 
among the drillers has brought the method and machinery to a high 
state of efficiency. 
The rotary is so entirely different from the old-fashioned cable rig 
and churn drill that it has been thought desirable to insert a brief 
account of the machinery and method. 
MACHINERY AND OPERATION. 
There are three styles of rotary drill in the field, differing slightly 
in details, but all working on the same principle. The form in most 
common use, the Chapman patent, has been taken for illustration. 
A general view of the derrick with machinery in place is shown in 
fig. 12, the rotary in PL X, A, and the hoisting and operating machin- 
ery in PI.' X, B. 
The method consists essentially in rotating a vertical drill rod, 
through which a continuous stream of water is forced downward. 
The drill rod is supported by a cable passing from a hoisting drum 
