"You don't miss much, siree," came the answer. "We've come face up against more than one tough job 'way up here at Culebra, and the question of the slope of our banks is one. You see, this trench will be mighty deep, and if we were to cut the sides perpendicular they would soon fall in. Most of the stuff's rock, of course, but it's queer rock at that. It's soft, weathers quickly, and becomes easily friable when water has got to it. So we've had to spread the banks wide, and make the slope easy, except where the rock's harder and allows a steeper slope. Now, guess we're near about the centre of the cut. You've seen what's happening to the north. Dirt trains run down the incline, enter the tracks of the Panama Railway, and run 26 miles to the dam at Gatun. South of us the tracks fall to the plain of the Rio Grande, and the spoil trains run down and dump their stuff on either side of the line the canal will take. You've got to remember that this trench is 'way up above tide level; so at the end of the cut, at Pedro Miguel, there is to be a lock, or, rather, a double lock--one for a vessel going north and one for a ship coming south. A matter of a mile farther along there is another lock--the Milaflores lock--double, like the last, but with two tiers. It will let our ships down into the Pacific. But you've got to remember that there is a tide in that ocean, so the lift of the Milaflores lower lock will be variable. Now, lad, come and see the rock drills." They descended into the bottom of the trench again, Phineas explaining that when it was completed there would be a bottom width of 200 feet, ample to allow the passing of two enormous ships. "Guess it's the narrowest part of the canal," he said, "though no one would call it narrow; but it's through hard rock, which is some excuse, and then this narrowest part happens to be dead straight. North of us the cut widens at the bottom to 300 feet, while elsewhere, outside the cut, the minimum width is 500 feet. You've got to bear in mind that I'm talking of bottom widths. Recollect that the banks slope outwards fairly gently, and you can appreciate the fact that the surface width of the canal stream will make a stranger open his eyes. Ah, here's a drill! This is the sort of thing you'll be doing." To the novice the machine to which Phineas had drawn attention was indeed somewhat curious. It looked for all the world like an overgrown motor car, constructed by an amateur engineer in his own workshop, and out of any parts he happened to have by him; for it ran on four iron wheels with flat tyres, and bore at the back the conventional boiler and smokestack. In front it carried a post, erected to some height, and stayed with two stout metal rods from the rear. The remainder of the machine consisted of the engine and driving gear which operated the drills.