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
Transpeninsular Line halfway between Delmar and Mardela Springs, Maryland. This marker is also the southern endpoint of the Mason–Dixon Line. Transpeninsular Line The Transpeninsular Line (at approximately 38°27′ N) is a surveyed line, the eastern half of which forms the north–south border between Delaware and Maryland. The border turns roughly north from the midpoint of the line towards the Twelve-Mile Circle, which forms much of the remainder of the Delaware land border. In 1751, a line was surveyed straight across the Delmarva Peninsula beginning at what at least some early Swedish settlers called "Cape Hinlopen", which was to be the southern boundary