Now, as the reservoir must be full at starting, and would then be eighty feet deep in the center, and a mile long, and a quarter of a mile broad, on the average, an embankment of uncommon strength was required to restrain so great a mass of water; and this was what the Hillsborough worthies were curious about. They strolled out to the works, and then tea was to come out after them, the weather being warm and soft. Close to the works they found a foreman of engineers smoking his pipe, and interrogated him. He showed them a rising wall, five hundred feet wide at the base, and told them it was to be ninety feet high, narrowing, gradually, to a summit twelve feet broad. As the whole embankment was to be twelve hundred feet long at the top, this gave some idea of the bulk of the materials to be used: those materials were clay, shale, mill-stone, and sandstone of looser texture. The engineer knew Grotait, and brought him a drawing of the mighty cone to be erected. “Why, it will be a mountain!” said Little. “Not far from that, sir: and yet you'll never see half the work. Why, we had an army of navvies on it last autumn, and laid a foundation sixty feet deep and these first courses are all bonded in to the foundation, and bonded together, as you see. We are down to solid rock, and no water can get to undermine us. The puddle wall is sixteen feet wide at starting, and diminishes to four feet at the top: so no water can creep in through our jacket.” “But what are these apertures?” inquired Grotait. “Oh, those are the waste-pipes. They pass through the embankment obliquely, to the wear-dam: they can be opened, or shut, by valves, and run off ten thousand cubic feet of water a minute.” “But won't that prove a hole in your armor? Why, these pipes must be in twenty joints, at least.” “Say fifty-five; you'll be nearer the mark.” “And suppose one or two of these fifty-five joints should leak? You'll have an everlasting solvent in the heart of your pile, and you can't get at them, you know, to mend them.” “Of course not; but they are double as thick as ever were used before; and have been severely tested before laying 'em down: besides, don't you see each of them has got his great-coat on? eighteen inches of puddle all the way.” “Ah,” said Grotait, “all the better. But it is astonishing what big embankments will sometimes burst if a leaky pipe runs through them. I don't think it is the water, altogether; the water seems to make air inside them, and that proves as bad for them as wind in a man's stomach.” “Governor,” said the engineer, “don't you let bees swarm in your bonnet. Ousely reservoir will last as long as them hills there.” “No, doubt, lad, since thou's had a hand in making it.” The laugh this dry rejoinder caused was interrupted by the waitress bringing out tea; and these Hillsborough worthies felt bound to chaff her; but she, being Yorkshire too, gave them as good as they brought, and a trifle to spare.