Caisson

During the construction of the viaduct, the sinking of the caissons in the river bed caused much difficulty to the engineer and contractors, as a bed of running sand was encountered; in consequence, the expenditure for these foundations proved almost prohibitive.

Caissons were enclosed dry chambers built on river beds to facilitate the construction of bridge piers.

Over hill, over dale / As we hit the dusty trail, / And those caissons go rolling along.