Wallace Line by the Sahul Shelf to New Guinea. The biogeographic boundary known as Lydekker's Line, which separates the eastern edge of Wallacea from the Australian region, has a similar origin to the Wallace line. During ice age glacial advances, when the , both Asia and Australia were united with what are now islands on their respective continental shelves as continuous land masses, but the deep water between those two large continental shelf areas was, for over 50 million years, a barrier that kept the flora and fauna of Australia separated from those of Asia. Wallacea consists of islands that were not
Illinois–Indiana State Line Boundary Marker status on September 4, 2002. Illinois–Indiana State Line Boundary Marker The Illinois–Indiana State Line Boundary Marker is a sandstone boundary marker obelisk located near the end of Chicago's Avenue G, just west of the State Line Generating Plant of Hammond, Indiana. Since 1988 it has been north of the Wabash River. The obelisk was constructed by the Office of the United States Surveyor General ca. 1838. In 1988, the marker was relocated north of its original location, but the structure continues to straddle the state line between Illinois and Indiana. As one of the earliest structures still standing in Chicago,