3 feet span. It is support- from the top of this backing to the crown of the main arch, were of white oak and spruce, from twelve to fifteen ed on stone abutments ? feet thick at street grade, 4 feet at the spandrels are filled with concrete, plastered with half an feet in length and twelve inches… … viaduct, from the waiting rooms to two covered landings on The foundations of these arches are first class gneiss rub- Fig. 20._THE UNDERGROUND RAILWAY, NEW YORK CITY,—END ELEVATION OF THE VIADUCT. top of the viaduct. The waiting room is on a leve? with the ble masonry, and project one foot beyond…
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