In metalmines the main passages are known as levels, and these are connected at intervals by winzes or small shafts.
The working-floors are connected by winzes with the main haulage roads below.
These winzes serve for ventilation, for the passage of the workmen, and for chutes through which the ore is dumped to the level below.
In the meantime a new level and a system of haulage roads have been driven a hundred feet below, and winzes have been driven upward to connect with the old level which is to be abandoned.
Work is then started on the floor above, the upper floors being connected with the main haulage roads by winzes which are maintained through the filled ground.