pt. 1. History of the explorations of the cañons of the Colorado [May 24-Sept. 20, 1869] Report on a trip to the mouth of the Dirty Devil River [May 27-July 11, 1872] by A.H. Thompson.--pt. 2. On the physical features of the valley of the Colorado.--pt. 3. Zoology: Abstracts of results of a study of the genera Geomys and Thomomys, by Elliott Coues. Addendum A. The cranial and dental characters of Geomydæ, by Elliott Coues. Addendum B. Notes on the salamander of Florida (Geomys Tueza) by G.B. Goode.