One was in a tropic country one time after an all-night march to a river where the ferry was a water-soaked bamboo raft. They had to wait until some native might happen along with a bull--or it might be a cow--to tow the raft across. After crossing the river twice in that day, the young marine commander halted on the bank and said: "That's sure not crossing in a hurry if we had to. Might's well go to it and build a bridge right now." They cut down trees, got a portable pile-driver from their transport, rigged it up and set to work. They hoisted the hammer--a good heavy one--and let it drop. Bam! she struck, and into the mud for about two feet went the pile. Fine! They hoisted the hammer again--four men hauling on pulley blocks did the hoisting--and let her go again. This time instead of a fine bam! the hammer went a fine splasho! into the river. The great heat and dampness of the place had warped the runways; almost every other time they let that hammer drop, it jumped the runways and into the river. But that was all right. They could fish her out and hoist her up by man power again. It was when they left the solid bank and had to put out into the river that their troubles began. A pile-driver ought to have a pretty solid foundation. Ought to have! They took two dugout canoes, lashed them together, put a bamboo deck across, set their pile-driver on the deck and turned to again. It made a kind of a wabbly base; besides hauling the hammer out every time it jumped into the river, they had to see that it didn't come bouncing down atop of their own heads or through the canoe deck. However, they were getting action. They finished driving the piles and setting up the stringers. For their bridge floor they laid down wood shingles, and over that a mat made out of woven bamboo strips. For a top deck? Well, it was a coral island and the roads of that country were of pounded coral; they put a top dressing of pounded coral across the bridge. And then the young marine commander looked her over and figured on the dimensions of his struts and stringers, and said: "Some class! She'll stand a two-ton load." And then along came a steam-roller from off the transport, and the roller weighed five tons and it was important that it be passed across. "Go ahead," said the marine commander--"only I hope you can swim!" And they all camped on the bank to watch. The steam-roller man was an optimist and a literary person: "You may have builded better than you know, captain!" The bridge settled down another foot, but the roller got across, and back and over many more times; which set the younger marines to standing on the bank and saying: "That's us--bridge builders!"