a. The height of ore available above a given working level. If the orebody
has been proved by shaft sinking to a depth of 300 ft (91 m) from the
surface, the orebody is said to have 300 ft (91 m) of backs.
See also: back
b. A quarryman's term for one set of joints traversing the rock, the other
set being known as cutters. Nelson
c. A system of joints in coal or stratified mineral oblique to the bedding
at an angle of 35 degrees to 75 degrees . See also:
slips BS, 11
d. Slips; used to denote a slip met with first at floor level.
Dictionary of Mining, Mineral, and Related Terms