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
Purchase line at present-day Cherry Tree, Pennsylvania. This was agreed to as the "nearest point" of the treaty. This became the tri-point between present-day Clearfield, Cambria, and Indiana counties, although the borough of Cherry Tree, Pennsylvania was later included entirely in Indiana for convenience. The line is still a boundary through most of its length: in Armstrong County running ESE from Kittanning it separates the townships of Rayburn and Valley (north) from Manor and Kittanning (south). There is gap through the town of Cowanshannock, but at the knick point of the boundary between Armstrong County and Indiana County the line begins again,