LETTEE. 5 



The area assigned to this party is limited on tlie north by the paral- 

 lel of latitude of 39° 15' ; on the south by the parallel of 38° 30' ; on the 

 east by the eighth guide-meridian of the land-survey, and on the west by 

 the one hundred and seventh meridian. 



The party left Denver on May 29, and commenced field-work on June 1, 

 and ended October 21. The secondary triangulation and the topograph- 

 ical work of the district were completed, with the exception of a part 

 of the country in the immediate neighborhood of the North Fork of the 

 South Platte, and a small area on Ten-Mile Creek, which will be 

 completed early this season. 



In the prosecution of the topographical work, ninety-six stations of 

 sufficient importance to be numbered were made, besides a large num- 

 ber, twenty-five or thirty, of minor importance, for obtaining local 

 details, &c. ; nine peaks exceeding 14,000 feet in elevation, and a very 

 large number of peaks exceeding 13.000 feet, were measured as accur- 

 ately as possible by barometer or theodolite. All the important passes 

 in the mountain-ranges within this district were examined. 



During the winter and spring, in the office, Mr. Gannett has made a 

 map on a scale of two miles to one inch, in 200-foot contours of the 

 area worked, and has also reduced the hypsometric work of the season. 

 He has prepared for the press a new edition of the ^' Lists of Elevations 

 Westof the Mississippi Eiver," (which will contain about 75 octavo-pages,) 

 and has prepared a short geographical report, and a short memoir on 

 the results of the trigonometric leveling carried on during the past 

 season. 



Doctor Peale, the geologist of the South Park division, was assisted by 

 Mr. W. E. Taggart, and their plan of work was as follows : One per- 

 formed the detailed work at or near camp, such as making measured 

 sections, collecting fossils, &c., while the other accompanied the topo- 

 grapher to the station selected for the day's observations, which was 

 generally the highest point in the immediate region. At the latter 

 place, the boundaries of the geological formations were defined in colors 

 on a drainage-sketch; this was, of course, based on previous detailed 

 work. In this manner, the geologist was able to make much more per- 

 fect results than he could otherwise have done. The amount of labor 

 thus performed by this party was very great, and reflects great honor 

 on the survey. 



The labors of Mr. J. T. Gardner during the season of 1873 have shown 

 the importance of careful instrumental observation in raising the stand- 

 ard of the toi)Ographical work of the survey. His methods will be 

 explained more fully by himself in a subsequent portion of this report. 



The primary triangulation during the season of 1873 covers about 

 17,000 square miles. Over two-thirds of this area the triangles are 

 completed, and the third angles of the remaining triangles will be ob- 

 served this season. 



Sixteen stations were visited and the angles at them repeatedly 



