This was the lock below where the Aquashicola creek emptied into the Lehigh River. The canal itself did not run through the gap; it was open water for canal boats. For more information, see http://www.loc.gov/pictures/item/pa1877/
In the 1970s, this is what was left of the aqueduct which carried the Lehigh Canal over the Aquashicola Creek. The Central of New Jersey trestle is visible in the background.