Wild areas are being rapidly reduced in size in the United States, especially in the vicinity of large cities, and the preservation of sanctuaries in metropolitan districts is worthy of note. The Greenbrook Sanctuary is included in the New Jersey section of the Palisades Interstate Park, which overlooks the Hudson River. The author has made a careful study of the 150-acre tract, describing geology, soils, climate, land use history, the various biotic communities, and animal factors. Folded maps show topography, trails, and plant communities.