Produced by Larry B. Harrison, Josephine Paolucci and the Online Distributed Proofreading Team at http://www.pgdp.net. NUMBER 123 JULY 10, 1922 OCCASIONAL PAPERS OF THE MUSEUM OF ZOOLOGY UNIVERSITY OF MICHIGAN ANN ARBOR, MICHIGAN PUBLISHED BY THE UNIVERSITY THE MAMMALS OF WASHTENAW COUNTY, MICHIGAN BY NORMAN A. WOOD Three natural physiographic divisions cross Washtenaw County from northwest to southeast. The northwestern part of the county is occupied by the rough interlobate moraine of loose-textured soil, the Interlobate Lake District; a broad Clay Morainic Belt occupies most of the central part of the county; and in the southeastern corner of the county is found a low Lake Plain, once the bed of glacial Lake Maumee. The Interlobate Lake District has a conspicuous system of moraines, making up a most irregular land surface. Steep knolls 100 to 200 feet in height are closely associated with basins, which are often deep, and some of which are occupied by lakes. Small, undrained depressions occur everywhere, producing thousands of acres of swamp and marsh land. The Clay Morainic Belt occupies the region from just below Portage Lake to Ypsilanti. It is composed of glacial till plains and clay moraines extending from northeast to southwest. This area includes the highest land in the county, one hill exceeding and several approaching 1100 feet in altitude. Most of the area is high and rolling. The old beach, marking the limits of the Lake Plain District, runs northeast from Ypsilanti to the county line above Cherry Hill, and southwest through Stony Creek to a point on the county line about eight miles west of Milan. The native upland forests of the Interlobate Moraine District were composed chiefly of red, yellow, and white oak, with some smooth-bark hickory and sugar maple and a few shag-bark hickories. Here were also large areas of creeping juniper and a few small patches of ground hemlock (yew). On the flood-plains of the rivers and lakes were quite extensive swampy forests of soft maple, black ash, and white elm. Swamp oak and whitewood grew commonly in the drier situations toward the edge of the swamp conditions. The red-bud and red cedar were characteristic of the river banks. White pine probably never grew in the county, although a few trees occur on the south bank of the Huron River near Hamburg, a few miles north of the county line. Tamarack bogs, some of large size, are abundant in the Interlobate Moraine District and occur commonly also in the Clay Morainic District, but are practically wanting in the Lake Plain District.