CHAPTER ly. 



NOTES ON TEIANGULATIONS AND MEASUREMENTS OF 



HEIGHTS. 



Parallel 40^" 30' forms the most northern line of the area surveyed in 

 Colorado, by Dr. 'F. Y. Hayden's United States Geological and Geograph- 

 ical Survey of the Territories, during the years 1873-1876, while paral- 

 lel 40° 15' is the southern line of the work performed by Clarence King's 

 Survey of the Fortieth Parallel, during the years of 1867-1872. 



A net-work of triangles was expanded over the respective districts of 

 the two separate surveys in the usual manner, in each case from care- 

 fully measured base-lines. The base-lines of Clarence King were situ- 

 ated near Fort Steele and Sherman Station, on the Union Pacific Eail- 

 road, while thoseof Dr. Hayden's United States Geological and Geograph- 

 ical Survey were measured near Denver, Col., and in the San Luis Park. 



It might reasonably be presumed that in the expansion of primary as 

 well as secondary triangles, from bases several hundred miles apart, with 

 only natural objects used as sighting-points, the accumulation of error 

 would be exceedingly large at those portions of the area the most distant 

 from the base lines, and in the plateau country where good sighting 

 points become scarce would necessitate a large correction. 



It is evident that the most practical test of the accumulation or non- 

 accumulation of error would be the comparison of points determined by 

 Professor Hayden's United States Geological and Geographical Survey, 

 with the same points determined by the geodetic corps of Clarence 

 King's Survey of the Fortieth Parallel during the years 1867-1872. 



With no little satisfaction we are able to state that between the two 

 surveys starting from different base-lines the coincidence of points is 

 remarkably close ; so close, indeed, that on the scale adopted by us for 

 the publication of maps the difference is scarcely apparent. 



Being supj)lied with all the maps bearing the stamps of official publi- 

 cation — with a view of comparing data — we found, as far as comparisons 

 of trigonometric work were concerned, that the location of points from the 

 Survey of the Fortieth Parallel alone were trustworthy, while the errors 

 of other published maps of that country were great and completely at 

 variance with the true relations and conditions of the surface. 



In the latter part of the year 1874 a barometric station was estab- 

 lished at the White River Indian agency by Mr. A. R. Marvir.e's division 

 of Dr. Hayden's United States Geological and Geographical Surveys of 

 the Territories, at which tri-daily observations were continued up to the 

 time our party left the district in the fall of 1876. On this base depend 

 our observations for altitudes throughout the district lying between the 

 Yampa and the White River. 



It is but fair to state that these heights cannot be considered irrefu- 



376 



