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busy for a while, discharging a volume of water as great as the daily supply required for a city the size of Atlanta. Care had to be taken, meanwhile, not to pump out sand along with the water, or the adjacent buildings would have come tumbling down, just as in a certain en- gineer's vision of the most effective way of destroying the city of Boston:

"An e n e m y need not bother mustering battleships or waste his time bombard- ing from afar the intellec- tual Hub of this land of ours. In time of peace let him have his spies build a big pumping station right in the middle of that city, and at the proper time start draw- ing indiscriminately from the ground below the water saturating the subsoil. You know a large number of Boston's big buildings rest upon floating foundations. Pmnp out the water in the supporting quicksand, and down those structures would t u m b 1 e into the yawning cavities so created. It would be far more effective in its demolition than the projec- tiles of a hostile fleet!"

Up near the north end of Manhattan Island, at Lex- ington Avenue and One hundred and Twenty-ninth Street, the subway diggers had to construct another stout waterproof floor when they encountered what evi- dently was once a swamp.

We mentioned, in passing. the razing of the old Astor Flouse, which was built upon sand. The tunnel which comes up Vesey Street and cuts under the site of the old hotel curves around into Broadway through big cylin- ders of cast iron.

Underground swamps and watercourses, sand, quick- sand, sand mixed with boul- ders (as in Brooklyn) — all these the diggers encounter and vanquish. But what the

��Popular Science Monthly

��subway builders fear most is something dift'erent from all of these: a material known to the geologist as Manhattan Schist and to the rest of us as "rotten rock." No material is more treacherous than this, for along' with layers of ex- treme hardness are pockets and seams of disintegrated stuff", some of it so soft that, after it has been exposed a little

���Under the old Astor House, which has been torn down because an underground swamp made it extremely hazardous to tunnel beneath the building. The illus- tration shows an underground dinner of celebration when a section of the iron tubes for one of the subway lines was completed. The arch of the big tubes shows in back of the posts at the left of the picture

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