LETTER TO CAPTAIN HUMPHREYS, TOPOGRAPHICAL ENGINEERS. 
Smithsonian Institution, Washington,'April 7, 1857. 
Sir : During the first organization of the parties for the survey of a railroad route to the 
Pacific, application was made to the Smithsonian Institution, by the officers in charge, for 
instructions and suggestions in reference to the development of the Natural History of their 
respective lines. These were cheerfully furnished as in accordance with the objects of an 
establishment intended for the increase and diffusion of knowledge. The specimens in zoology, 
as collected, were transmitted, from time to time, to the Institution and properly preserved, 
until the return of the parties. A series of special reports was prepared by the naturalists 
of the expeditions, but as these were necessarily disconnected and incomplete, it was deemed 
desirable to furnish a general systematic report upon the collections as a \yficd e j and for this 
purpose the materials were entrusted to competent individuals, the necessary drawings being 
executed by a skilful artist within the walls of the Institution. 
I now, transmit the first part of the general report—on the Mammals—which has been 
prepared by Professor Baird, Assistant Secretary of this Institution, and I trust the character 
of the work is such as to merit the approbation of the Department as well as to advance the 
interests of science. 
Very respectfully, your obedient servant, 
JOSEPH HENRY, 
Secretary Smithsonian Institution. 
Captain A. A. Humphreys, Topographical Engineers. 
