372 Noble — Geology of the Grand Canyon, Arizona. 



Indian village. Roads also lead to the towns of Williams and 

 Ash Fork, about 60 miles respectively south and southwest. 



Field Work. — The geological field work upon which the 

 thesis is based was begun upon the 23d of August, 1908, and 

 ended upon the 12th day of December of the same year. The 

 greater part of the work was done from a permanent camp on 

 the Shinumo, which served as a base of operations for studying 

 all the region in the greater depths of the canyon. Two trips 

 were made to the north rim. The first was made in September 

 and the second in November. Each trip lasted a week. Camp 

 was established in the Muav Saddle and excursions were made 

 from there over the surface of Powell Plateau and over the 

 Kaibab mainland as far as the head of the Shinumo Amphi- 

 theater. The writer was accompanied on these occasions, as 

 well as during his stay in camp on the Shinumo, by Mr. John 

 Walthenberg as guide, whose detailed knowledge of the region 

 and whose assistance in other ways were invaluable. The work 

 in the southern part of the area was done from Bass Camp, 

 from which point excursions were made over the Coconino 

 Plateau and into the upper part of the canyon. 



Literature. — Two references to the geology of the area are 

 to be found in geological literature : 



Captain Dutton in his monograph entitled " The Tertiary 

 History of the Grand Canyon District" (Dutton, a) describes 

 most fully and charmingly the geology of the north rim in 

 this section of the Grand Canyon. In Chapter YII he describes 

 the surface features and scenery of the Kaibab Plateau in the 

 vicinity of Point Sublime. Chapter VIII is devoted to the 

 panorama disclosed from Point Sublime, while Chapter IX 

 describes the walls of the amphitheaters of the north side in 

 detail. The Muav Saddle and Powell Plateau are described 

 on pp. 162-167, and the Shinumo Amphitheater on pp. 167-174. 

 His work, however, did not extend into the depths of the 

 canyon. 



Mr. J. S. Diller of the United States Geological Survey 

 describes in his report on the production of asbestos in " Min- 

 eral Resources for 1907" (Diller, a) the deposits of asbestos 

 occurring in the Algonkian sediments of this area near Bass 

 Ferry. This is the only reference in the literature to the 

 presence of Algonkian strata in this part of the Grand Canyon. 



Acknowledgments. — In 1901 Mr. Charles D. Walcott and 

 Mr. G. K. Gilbert spent several days at Mr. Bass's camp on the 

 Shinumo and at that time worked out the structure of the 

 pre-Cambrian sediments, which Mr. Walcott correlated with 

 the section described by him in Unkar Yalley (Walcott, <z, b, 

 <?, d, and e). His notes, however, are unpublished, and it is 

 due to his kindness and courtesy that the writer is enabled to 

 present the first description of the area. To Mr. Walcott the 



