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
Lew Wallace position and prevent the enemy from escaping and without Grant's authority to take the offensive. With the Confederates continuing to advance, Wallace led a second brigade to the right and engaged the Confederates with infantry and artillery. Wallace's decision stopped their forward movement and was key in stabilizing a defensive line for the Union troops. After the Confederate assault had been checked, Wallace led a counterattack that regained the lost ground on the Union right. On March 21, 1862, Wallace, McClernand, and C. F. Smith were promoted to major general for their efforts. Wallace, who was age thirty-four at the