REPORT OF A. D. WILSON, CHIEF TOPOGRAPHER. 



LETTER OF TEANSMITTAL. 



Office of the United States Geologigal and 



Geographical Survey of the Territories, 



Washington, D. (7., January 25, 1878. 

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

 triangulation of Colorado ; also, a description of methods of topograph- 

 ical, field, and office work. 



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

 until 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 fin- 

 ished the computations, giving the results in the appended report. 



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 unim- 

 portant errors may occur, but I endeavored to make it as perfect as pos- 

 sible. 



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. 



Appended to this report I give some observations on the magnetic 

 needle, illustrating the great range of the magnetic variation over the 

 State. Hoping that this report may prove of interest and meet with 

 your approval, 



I am, verv respectfully, your obedient servant, 



A. D. WILSON, 

 Chief Topogra/pher. 

 Dr. F. Y. Hayden, 



• United States Geologist in charge, 



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