These locomotives were flexible dual purpose machines.  They were logging  locomotives and they were "yarding" engines, used to "yard" or pull logs from the woods to a loading point near the track.

A large "bull" gear was mounted  forward of the boiler on the unit's extended frame.   On the right end of the gear's shaft was mounted a cable spool.   One end of a cable, or "wire rope" as it was called in those days, was attached to a log and the other cable end was attached to the spools.  A gear transmission clutch was engaged on the locomotive to "yard" or pull the log from where it lay to a loading point near the track. 

These type of locomotives  were nicknamed "gypsy" by the loggers.