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
Simson line Simson line In geometry, given a triangle "ABC" and a point "P" on its circumcircle, the three closest points to "P" on lines "AB", "AC", and "BC" are collinear. The line through these points is the Simson line of "P", named for Robert Simson. The concept was first published, however, by William Wallace in 1797. The converse is also true; if the three closest points to "P" on three lines are collinear, and no two of the lines are parallel, then "P" lies on the circumcircle of the triangle formed by the three lines. Or in other words, the Simson