(1,020,000 m3) of timber were removed from the Okefenokee by 1927, when logging operations ceased. The Okefenokee Preservation Society, formed in 1918, promoted nationwide interest in the swamp. With the support of state and local interests and numerous conservation and scientific organizations, the Federal Government acquired most of the swamp for refuge purposes in 1936. In 1937, with Executive Order 7593 (later amended by Executive Order 7994), President Franklin Delano Roosevelt established the refuge, designating it as "a refuge and breeding ground for migratory birds and other wildlife." The establishment of Okefenokee Refuge in 1937 marked the culmination of a movement that had been initiated at least 25 years earlier by a group of scientists from Cornell University who recognized the educational, scientific, and recreational values of this unique area. In 1974, to further ensure the protection of this unique ecosystem, the interior sections of the refuge were designated a National Wilderness Area. In 1986, the Okefenokee Refuge was designated by the Wetlands Convention as a Wetland of International Importance. Geography Okefenokee NWR has an approved acquisition boundary of 519,480 acres (2,102 km2), which is 123,480 acres (500 km2) larger than its current area. Approximately 371,000 acres (1,500 km2) of the Okefenokee Swamp wetlands are incorporated into the refuge. 353,981 acres (1,432 km2) within the swamp were designated as the Okefenokee Wilderness, a part of the National Wilderness Preservation System when the Okefenokee Wilderness Act was passed in 1974, making it the third largest wilderness east of the Mississippi River. The Okefenokee Swamp is a vast bog inside a huge, saucer-shaped depression that was once part of the ocean floor. The swamp now lies 103 to above mean sea level. Peat deposits, up to thick, cover much of the swamp floor. These deposits are so unstable in spots that trees and surrounding bushes tremble by stomping the surface. Native Americans named the area "Okefenokee" meaning "Land of the Trembling Earth". Swamp habitats include open wet "prairies", cypress forests, scrub-shrub vegetation, upland islands, and open lakes. The Okefenokee Swamp is one of the world's largest intact freshwater ecosystems. It has been designated a Wetland of International Importance by the United Nations under the Ramsar Convention of 1971. The swamp is compared through research to wetlands worldwide. It is world-renowned for its amphibian populations that are bio-indicators of global health. Water from the Suwannee River Sill area is used as a standard