National Geographic : 1911 Feb
are constructed to stand five years of continual use. For the main culverts in the side walls there are 21 forms in12-foot lengths, each form ©0 weighing not less than 14,443 pounds. There are 12 forms for the culvert in the middle wall, each 12 feet long and weighing not less than 14,750 pounds. There are loo forms for the lateral culverts, each o10feet long and weighing not less than 2,170 pounds. 14,75o pounds. There are IOO forms for tbhe lateral culverts, each IO feet long and weighing not less than 2,17o pIouds.