of the Cuzco Valley, Peru. 3 



assigned to the glacial epoch have been reported. 3 Time was 

 available, however, for a geologic reconnaissance including 

 certain detailed examinations of the western portion of the 

 Cuzco Valley, and the results of these observations are recorded 

 on the following pages. The geology is very complex, and the 

 time at my disposal was insufficient for the collection of the 

 data necessary for the solution of the many problems which 

 arose. A much larger amount of detailed work is required 

 before the geologic history of this interesting area can be 

 written. The present paper is therefore a contribution to the 

 geology of the Ouzco Valley, not a final report. 



Note on the topographic map. — The base map accompanying 

 this report (Plate I) is the first published sheet of a series 

 covering the field of operations of the Peruvian expeditions 

 of 1911, 1912, 1914, and 1915, conducted under the joint 

 auspices of Yale University and the National Geographic 

 Society. An effort has been made to produce maps of a high 

 degree of excellence, and credit is due to the chief topographer, 

 Mr. Albert H. Bumstead and his assistant, Mr. Osgood Hardy, 

 for the success attained in devising field methods for use in 

 this difficult area. 



The parallels and meridians of the Cuzco Valley map are 

 based on latitude and longitude established for the Cuzco 

 railroad station in 1914 by Mr. Bumstead, who describes his 

 method as follows : 



"Latitude observations were made at 8 located points of a system 

 of triangulation beginning near Cuzco and extending about 60 

 miles westerly and after reducing each to the Cuzco depot their 

 mean was adopted as the latitude of that point. The instrument 

 used was a small Berger transit reading direct to 30" and by 

 estimation to 10". In all 233 observations were made; 177 being 

 meridian altitudes of stars, 32 exmeridian altitudes of stars and 

 24 exmeridian altitudes of the sun. The probable error in the 

 latitudes of the several stations ranged from 1" to 9" with a 

 mean of 4"." 



All the latitude stations were on the highland between the 

 great canyons of the Urubamba and Apurimac rivers which 

 flow approximately parallel from east to west, and about 



s Gregory, Herbert E., The gravels at Cuzco, Peru ; this Journal, xxxvi, 

 pp. 15-29, 1913. In this paper the topography, structure, history, and 

 age of the enormous gravel fan on the edge of which the city of Cuzco 

 is built are discussed in detail, and they will not be further treated in 

 the present report. =\ 



