economically. Hoists are cable-operated devices which transport materials up an incline in cars.
Conveyors range in size, length and capacity, and may be a continuous belt inclosed in a housing,
or buckets traveling along a cable elevated on supports.
(2) Of the mobile equipment employed in many extraction industries, such heavy
equipment as cranes, bulldozers and power shovels is utilized in most of those industries involving
excavation. Trucks, or mine cars which may operate on temporary tracks, are used to bring the
raw material from the pit, quarry face, or mine.
(3) Complex equipment is not common in the extraction industries. A derrick is erected
at the site of a well to handle the pipe and tools while the well is being drilled. Afterwards the
derrick commonly is removed. Similar to derricks are the headframes found over shaft mines. A
headframe is the structure which supports the cables operating the mine elevator. Sometimes the
framework is apparent, other times the headframe is roofed or completely inclosed. If no waste is
piled nearby, the headframe may be the only indication of a shaft mine.
c. Buildings are few and small, or even lacking in the extraction industries. They rarely serve
functions essential to these industries, and therefore are not very useful to the IA. Buildings may
shelter crushing and screening equipment, they may be used to store mobile equipment or
explosives, or they may house personnel. On occasion administration buildings and workshops for
repairing equipment will be seen.
d. Open storage and waste may appear as either piles or ponds. Large piles of waste often
are associated with the extraction industries, especially mining, because it is necessary to remove
large quantities of worthless material to get out the ore or other useful material. Stored raw
materials usually can be distinguished from piles of waste since the waste is dumped in an area
and in such a manner that makes further handling difficult and accumulates there in ever-
increasing quantities. The raw materials, however, always are placed in a readily accessible
location, usually near a rail line or road, and stored in such a way that they can be economically
transshipped. Artificial ponds may be used to hold liquids such as crude oil or brine for salt
Excavations, if present, are the most significant class of image components for this
category. Open storage and waste also will be valuable in identifying an industry.
Equipment for handling bulk materials, such as conveyors, hoists and cranes, aid in
analyzing the succession of operations. Complex equipment, such as headframes and
derricks, at times are the only evidence of an extraction industry to be seen on aerial