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
Acephalous line Acephalous line An acephalous or headless line is a variety of catalectic line in a poem which does not conform to its accepted metre, due to the first syllable's omission. Acephalous lines are usually deliberate variations in scansion, but this is not always obvious. It is a technique employed often in the concluding lines of hymn texts, and has been employed in poetry to change tone or announce a conclusion, including its use in Joyce Kilmer's "Trees" and A. E. Housman's "To An Athlete Dying Young." Robert Wallace argues in his essay "Meter in English" that the term "acephalous line"