on the Navajo Reservation. 99 



latitude 40° is established, viz.: 4800 feet. Again the effect 

 of climatic conditions producing glaciation must have been 

 peculiarly localized -along the Arizona-Utah boundary. The 

 nearest known glacial materials are in the La Plata Mountains, 

 about 100 miles to the northeast at an elevation of 8500 to 

 8800 feet and at San Francisco Mountain, 160 miles to the 

 southwest where the terminal moraine of a glacier two miles 

 in length rests at an elevation of 9200 feet. Carrizo Mountain, 

 40 miles east of the garnet fields, and 4620 feet higher in eleva- 

 tion, and Skeleton Mesa, 35 miles west and about 3000 feet 

 higher, are without evidences of glaciation. Moreover the 

 association of materials composing the drift of the garnet fields 

 is unlike that reported elsewhere from Arizona, Colorado, New 

 Mexico, or Utah. 



(2) The statement of Sterrett, that " the garnet-bearing drift 

 deposits . . . are covered with a stratum of hard white sand- 

 stone,"* points to a pre-Quaternary period of glaciation not 

 elsewhere recognized in Arizona or Utah. 



The erratics on the border of the glaciated (?) areas described 

 by Sterrett and Woodruff were noted by the writer in 1910. 

 In 1913 the outer edge of the "drift" at Garnet Ridge was 

 mapped with the assistance of Mr. K. C. Heald, but the scar- 

 city of water and the demands of the work in hand permitted 

 no more than a superficial examination. During the past sea- 

 son a desire to examine the geologic features of the lower 

 Chinle Valley and to study the problem presented by the 

 glacial (?) deposits was realized in consequence of a grant from 

 the Dana Research Fund of Yale University. 



Geography, 



Three areas covered by erratics have been located, one south 

 and two north of the Arizona-Utah boundary line in longitude 

 109° 45' (see map, fig. 1). The southernmost field has a super- 

 ficial extent of about 1*2 square miles, but the erratics are 

 dominant only in a belt one-half mile long and one-fourth mile 

 wide at the eastern end of Garnet Ridge, f and on the other hand 

 isolated bowlders are to be found beyond the limits of the area 

 mapped. The Mule Ear field contains about *25 square mile, 

 in which bowlders are most abundant on the high ridge form- 

 ing the west wall of Mule Ear Pass. The erratics of the Moses 

 Rock field are strewn along a narrow, irregular belt six miles 

 in length. The commanding topographic feature of the region 

 is " the Comb," a euesta which forms the eastern boundary of 

 Monument Yalley. The face of the euesta is a wall of massive 



* Loe. cit.. p. 825. 



f The topographic and geologic ternis appearing in this article are those 

 adopted for use in forthcoming reports on the Geography and the Geology of 

 the Navajo Eeservation. 



