[Illustration: THE HACKENSACK PORTALS OF THE PENNSYLVANIA'S GREAT TUNNELS UNDER NEW YORK CITY] But your interest in the man who was blown from the tunnel to the surface of the river and escaped with his life is not entirely satiated, and you ask more questions. What do they do when they strike soft mud like that? "We get down and pray," he of the experience in this weird form of construction engineering tells you. "We try to get the boys safely back through the air-lock, and then we quit boring till we can fix things up from outside. If it's a real bad case we've got to make land to bore through. It's generally done by dumping rock and bags of sand from floats just over where she blows out. It's a pretty rough way of doctoring her up, but it has to go, and generally it does. All we want is to get it to hold until we can set the rings of the tunnel. "That ain't always the worst. I've been driving a bore under water this way, when we struck stiff rock overhead and soft mud underneath the edge. That's something that makes the engineers hump. You can't rest a cast-iron tunnel like this on mud and you get a wondering if you've got to quit after all this work under the durned old river, and let the boss lose his money. "The last time we struck a snag of that sort, the boss didn't give up. He wasn't that kind. He had a chief engineer that was brass tacks from beginning to end. What do you suppose that fellow did? He bored holes in the bottom of the lining and drove steel legs right down to the next ledge of solid rock below. There's that tunnel to-day, carrying 32,000 people between five and six o'clock every night perched down there seventy feet underground like a big caterpillar sprawled under the wickedest ledge o' rock you ever see." It takes a real genius of an engineer for this sort of work. He who drives his bore into the unknown must be on guard for the unexpected. Emergencies arise upon the minute, and the tunnel engineer must be ready with his wits and ingenuity to meet them. Finally the day does come when the bores from either shore are hard upon one another. If there has been blasting under the bed of the river it is reduced to a minimum. The drills work at half-speed, the fever of expectancy hangs over the men. Those who are close at the heading catch faint sounds of the workmen on the other side of the thin barrier--the last barrier of the river that was supposed to acknowledge no conqueror.