The young engineer explains--in some detail. To find a foothold for this building was no sinecure. Tests with the diamond drill had shown that solid rock rested at a depth of 145 feet below street level at the south end of the plat. At the north end, the rock sloped away rapidly and so that part of the building rests upon compact sand. The rock topography of Manhattan island is uncertain. There are broad areas where solid gneiss crops close to the street level, others where it falls a hundred feet or more below water level. There is a hidden valley at Broadway and Reade street, a deep bowl farther up Broadway. Similarly, the north extremity of the Municipal Building rests upon the edge of still another granite bowl--the sub-surface of that same Collect Pond upon which the New York boys used to skate a century or more ago. "That bothered some folks at first," laughs the engineer, "but we met it by sinking the caissons. We've more than a hundred piers down under this structure hanging on to Mother Earth. You don't realize the holding force of those piers," he continues. He turns quickly and points to a fourteen story building off over the trees of City Hall park. Out in one of the good-sized towns of the Middle West people would gasp a little at sight of it--in New York it is no longer even a tower. "Turn that fellow right upside down into the hole we dug for this building," says the engineer, "and the rim of his uppermost cornice would about reach the feet of our own little forest of buried concrete piers." That was one detail of the construction of the building. Here is another; the first six stories of the new structure involved elaborate masonry, giant stones, much carved. From the seventh story the plain walls of the exterior developing into an elaborate cornice were of simple construction. If the setting of these upper floors had waited until the first six stories of elaborate stonework had been made ready there would have been a delay of months in the construction work. So the contractor began building the walls--which in the modern steel skyscraper as you know form no part of the real structure but act rather as a stone envelope to keep out hard weather--from the seventh story upward. Eventually the masons working on the first six stories, working upwards all the time, reached and joined the lower edge of the masonry that had been set some weeks before. Time had been saved and you know that time _does_ count in New York. Remember the Wall street man who preferred to have his ribs crushed and his hat smashed down over his nose in the subway rather than lose ten minutes each day in the elevated.