ART. XXVIII.-NOTES ON THE GEOGRAPHICAL WORK OF THE 

 UNITED STATES GEOLOGICAL AND GEOGRAPHICAL SURVEY 

 OF THE TERRITORIES. 



By A. D. Wilson, 



Chief Topographer. 



[Plates 35-39.] 



Office op the United States Geological and 

 Geographical Survey of the Territories, 



Washington, D. C, April 16, 1877. 

 Sir : I have tlie honor to transmit herewith my report on the primary 

 triangulation of Colorado; also, a description of the methods of the topo- 

 graphical field and office work. 



The primary triangulation was in charge of Mr. James T. Gardner 

 nutil the fall of 1875, when, on his resignation, the continuation of the 

 work devolved upon me. 



I completed the field-work during the summer of 1876, and have 

 finished the computations, giving the results in the appended report 

 omitting minor details. 



Owing to the unfinished condition of the work when placed in my 

 hands, and the difficulties met with in going over an immense amount 

 of material with which I was not familiar, it is possible that some 

 unimportant errors may occur ; but I endeavored to make it as perfect as 

 X)ossible. 



I have attempted to give a general idea of the geographical work in 

 as concise a form as possible, designing only to convey some idea how 

 the geographical work of the survey has been carried on, and to show 

 upon what evidence our final maps rest. Hoping, that this report may 

 prove of interest and meet with your approval, 



I am, very respectfully, your obedient servant, 



A. D. WILSON, 

 Chief Topographer 

 Dr. F. V. Hayden, 



United States Oeologist iti-charge. 



