Washington prime meridian. "Entered according to Act of Congress, in the year 1850, by Thomas, Cowperthwait & Co., in the clerks Office of the District Court of the Eastern District of Pennsylvania." Includes list of steam boat routes with distances. 30. in upper right margin. Inset: Western part of michigan [ca. 1:3,000,000] 1 map: col.; 34 x 27 cm This map is in the public domain. Please attribute access and use of this digitized map to the Stephen S. Clark Library, University of Michigan Library.