Only several miles from Lake Erie, canal engineers faced the natural barrier of the Niagara escarpment, whose blue limestone rock rose thirty feet too high for a canal channel that had to flow downhill from the lake to keep boats afloat. With no viable alternative, for three miles one thousand two hundred workers, including many Irish immigrants, carved a trough through the hard rock. After months of backbreaking labor and countless explosions requiring tons of gunpowder, the Deep Cut became the last, most difficult, and costliest section of the original Erie Canal. This work delayed the canal's completion until 1825, one year after navigation was possible to the east and west. Despite the time required, the Deep Cut remains one of the canal's greatest engineering achievements. Its later excavation during Barge Canal construction in the early 1900s also required massive rock removal, though modern steam shovels and dynamite made that job less formidable.