''The sea has been divided.'' So marvelled a journalist describing the January day in 1912 when the final stretch of the Florida East Coast Railway opened, connecting Miami with Key West, 156 miles and plenty of blue water away. One of the truly great engineering feats of the last century, the island-hopping construction project took seven years to complete, cost dozens of workers their lives, and succeeded only because of the tenacity (and personal fortune) of Henry Flagler, an intensely private oil tycoon who, in his 80s, still dreamed of building another empire. Nature, it turns out, had other ideas: Just 22 years later, Flagler's rail was buried and destroyed during the Labor Day hurricane of 1935. Standiford skillfully unearths a forgotten tale of overreaching ambition and sandblasted ruin.