INTRODUCTORY LETTER. 
BY A. L. HEERMANN, M. D. 
Philadelphia, October 6, 1854. 
Sir : I herewith have the honor to submit to you the report on the natural history of that 
portion of California over which your command passed, during the late survey, from San 
Francisco to Fort Yuma. 
From the limited time within which it was desirable it should he completed, I have only 
undertaken the detail of the ornithological branch; the others I have placed in the hands of 
the following gentlemen : 
Professor S. F. Baird has classified the mammals. These are necessarily few; the great 
difficulties which present themselves in their preparation, added to the still greater one of their 
transportation when prepared, form insuperable obstacles to an extensive collection in this 
interesting department. 
Dr. Edward Hallowell has described the reptiles, among which he has found many new and 
interesting species. 
Mr. E. Durand and Dr. T. Hilgard have classified the collection of plants, consisting of about 
one hundred species, nearly twenty of which are new. 
Professor C. Girard has described many new species of fish, among which are several vivipa¬ 
rous ones from the coast of California. 
To all of these gentlemen I feel under deep obligations for the zeal with which they have 
entered upon their various branches of natural history, and the material assistance which they 
have afforded me in the early rendition of my report. 
As the maladies encountered during the course of the expedition, taken in time, were never 
allowed to assume a serious nature, I have made no medical report. They consisted of diseases 
incident to the country, and to camp life, such as intermittent fever, diarrhoea, and dysentery, 
besides some few surgical cases of incised and punctured wounds, all of which, however, termi¬ 
nated favorably. 
I remain, sir, your obedient servant, 
Lieutenant R. S. Williamson, 
Topographical Engineers , 
A. L. HEERMANN, M. D. 
Surgeon and naturalist to the command. 
Washington , D. C. 
