express astonishment at the figure, but it would not have impressed me as anything very extraordinary had he said billions instead of millions, because the figures were far beyond my comprehension. So I said nothing, and Will only said “U-m,” in a very matter-of-fact way.
“U-m,” mimicked Mr. Porter; “it does n’t seem to impress you very much, let ’s put it another way. Suppose you should dump all this material in Broadway. You would choke the street from Bowling Green to Spuyten Duyvil to a depth of over two hundred feet. There, I thought I would astonish you!” laughed Mr. Porter, as he saw our mouths open with surprise; “but it ’s true.
“See what a bullaballoo they are making over the Panama Canal, and yet all their excavation will not amount to much more than two hundred million cubic yards in a canal forty-five miles long, while we, with our seven-mile-under-water canal, have just about one third of that amount to haul out, Why, boys, if this channel was being excavated on land where you could see its depth and width, the papers would be full of it, and we would be having crowds of sight-seers out to watch the work, But we go on quietly, making no fuss and bluster, digging a channel nearly as wide as Central Park, and as long as from City Hall to One-Hundred-and-Twenty-fifth Street.”
“And has all this work been done with only one dredge-boat?” Will asked,
“Oh, not we have had four here up to a short time ago. Now the work is nearly done, so there are only two of us here in the bay. The other dredge has just left us to help out with the work on the Rockaway Inlet. Yes, the work has gone on steadily night and day, year in and year out. We come in to our dock on Saturday afternoons and have Sunday ashore, but you will find us here at any other time, plodding along and sticking to it, rain or shine. Nothing but a howling gale drives us to shelter.”
All this time, the boat was steaming back rapidly up the channel. Just before we reached the spot that was to be dredged, Mr. Porter bade us look over the side of the vessel and see the enormous suction-pipes. There were two pipes, one at each side of the boat, and while we were going along, they were raised out of the water. We had not seen them before because the vessel was loaded so heavily that they were submerged. The pipes were twenty inches in diameter, and, where they entered the hull, they were fitted with swivel-joints. At the opposite end of each pipe, there was a “drag,” or a sort of mouthpiece, about five feet broad, and partitioned off so that the openings in it measured about eight by nine inches.
“Anything that can go through those openings,” explained Mr. Porter, “will go through all the rest of the system, No matter how heavy it is, the water will carry it right up into the bins,”
“Suppose you should strike a rock bigger than eight by nine inches,” I asked; “what would you do?”
"We would just dig a hole in the sand and bury it.”
“Bury it!” I ejaculated.
Mr. Porter's eyes twinkled, “I astonished you again, did n't 1? There are lots of stone piles along this channel. Nobody ever thought that the channel would be dug through here, and there used to be no regulation against dumping rock in the bay. We can't suck up that rock because there is too much of it, and the pieces are too large, so, as I say, we bury it, All we do is to dredge a deep hole around the stone pile fifteen or twenty feet deep, and then the survey-boat comes along with a water-jet that loosens up the pile, and topples it over into the hole.”
We looked puzzled. “Yes,” explained Mr. Porter, “they play a stream of water on the pile just as you might play the garden hose on a sand-hill. You can use the water-jet under water as well as anywhere else.”
Presently we saw the drag lowered into the water. The pumps were started, and enormous streams of water poured, boiling and churning, out of the square conduits at each side into the bins. Soon the water turned muddy, but the river of sand we expected to see failed to appear.
“Is that what you pump up through the dredges?” Will asked.
“Yes, it is mostly water, but soon the bins will fill up, and then the water will flow over the top into an overflow channel, while the sand and mud settle to the bottom.”
Mr. Porter took us below and let us sec the big pumps at work. There were two centrifugal pumps about ten feet in diameter, driven by 450-horse-power engines, very now and then, we heard a bang and a crash as a large stone was carried through by the torrent of water, while there was an almost incessant rattle of small stones through the pipes. It was extremely interesting, and quite marvelous to think of those two drags groping blindly along the bottom, devouring everything that came within their reach. Mr. Porter explained that the boat had to keep moving lest the tide or some current carry it backward, jamming the suction-pipes, and breaking them.
When we got back on deck, we found, much to our regret, that the tugboat had returned, and we had to cut our visit short.
(To be continued.)
