Islands in Deep TimeHilltops surrounded by farmland in southern Wisconsin turn out to be the eroded remnants of an ancient archipelago. An island in the Yellow Sea where Korean tourists flock is the peak of a flooded mountain rising from a drowned continental shelf. From a mountaintop shrine to Genghis Khan in Inner Mongolia, the silhouette of a Silurian seascape can be spotted. On the shores of Hudson Bay, where polar bears patrol the Arctic tundra, a close look unveils