National Geographic : 1911 Feb
ANOTHER VIEW OF THE AERIAL CABLEWAYS USED AT THE GATUN LOCKS: LOOKING NORTH FROM EAST BANK, AUGUST 25, 1909 This illustration shows the early stages of the construction of these locks. The two "squares" on the left are timber forms inwhich concrete was laid in sections for the foundations. The uprights on the right are old French railsimbedded inthe concrete toreinforce the floor. The floor of the Gatun locks varies in thickness from 13 to 20 feet of solid concrete reinforced with these rails.