370 Noble — Geology of the Grand Canyon, Arizona. 



Colorado River at the foot of Bass Trail. Although only a 

 few hours were spent in the vicinity, the diagrammatic sim- 

 plicity with which the structural relations were revealed was 

 such that the interest could be immediately realized. In the 

 summer of that year the writer returned with the intention 

 of making a detailed study of these pre-Cambrian rocks. He 

 speedily found that the interest in this part of the Grand 

 Canyon did not end with the study of the pre-Cambrian alone : 

 it was found that the line of displacement of the "West Kaibab 

 fault which runs into the Grand Canyon at this point was itself a 

 remarkable structural feature and worthy of considerable atten- 

 tion ; that the entire Paleozoic section of the canyon wall was 

 here, as elsewhere, undescribed in absolute detail ; and finally 

 that there were problems of physiographic interest in the Grand 

 Canyon region the ultimate solution of which could be greatly 

 helped by a detailed study at this point. It was therefore de- 

 cided to extend the work to a complete area! study of the 

 region, including for this purpose the greater part of the new 

 Shinumo topographic sheet of the United States Geological 

 Survey. This report, accompanied by an atlas containing the 

 geologic maps, sections, and plates, was presented to the faculty 

 of the Graduate Department of Yale University in June, 1909, 

 as a thesis in partial fulfillment of the requirements for the 

 degree of Ph.D., under the title of " The Geology of the 

 Shinumo Area, Grand Canyon, Arizona." 



It is intended to present the substance of the thesis in two 

 or more articles in this Journal. The entire report is to be 

 published in extenso at a later date as a Bulletin of the United 

 States Geological Survey. For this reason, as well as because 

 of the large scale and elaborate nature, the geologic map, sec- 

 tions, and plates will not be published here. 



The first article will be presented in two parts. Part I, now 

 published, comprises a general introductory description of the 

 Shinumo area and deals with the basement rocks of the Archean. 

 Part II, to follow in a later number, will be devoted to the 

 Algonkian rocks of the Grand Canyon series and will include 

 a map showing the distribution of the Vishnu and Grand 

 Canyon series in the Grand Canyon. 



It is also proposed to devote a later article or articles to the 

 Paleozoic section of the canyon wall ; to a structural study of 

 the area, including both the pre-Cambrian and later structure 

 and a study of the displacements on the line of the West 

 Kaibab fault ; and finally to features of physiographic interest 

 in the area, — such as the drainage system of the plateaus and 

 the origin of the Esplanade and Tonto platforms. 



