Wallace Line to the west of the Philippines. Wallace's studies in Indonesia demonstrated the emerging theory of evolution, at about the same time as Joseph Dalton Hooker and Asa Gray published essays also supporting Darwin's hypothesis. Understanding of the biogeography of the region centers on the relationship of ancient sea levels to the continental shelves. Wallace's Line is visible geographically when the continental shelf contours are examined; it can be seen as a deep-water channel that marks the southeastern edge of the Sunda Shelf which links Borneo, Bali, Java, and Sumatra underwater to the mainland of southeastern Asia. Australia is likewise connected
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