510 Noble — Geology of the Grand Canyon, Arizona. 



entirely limestone, u b" is alternating limestone, and " d" 

 predominantly shale. Thus there are four major cycles of 

 oscillation upon which the minor cycles are superimposed. 



A comparison of the above section in the East Wash with a 

 section measured in the Asbestos Canyon, four miles to the 

 west, is of interest. In the Asbestos Canyon the " basal white 

 limestone" (a) has a thickness of 30 feet contrasted with a 

 thickness of 6 feet in the East Wash. The lower stratum of 

 "nodular, cherty limestone " is there V 9", contrasted with 

 V 6" in the East Wash. The upper stratum of "parallel- 

 banded, cherty limestone " is 22' 3" in the Asbestos Canyon, 

 containing in the middle an intercalated layer of purple shale, 

 and near the top a thin layer of rather fine arkose conglomerate. 

 The " argillaceous and calcareous red shales and limestones " of 

 division "&" have a thickness of 88 feet in the Asbestos 

 Canyon contrasted with 85' 5" in the East Wash. They do 

 not have the red color that characterizes them in the East Wash, 

 but are purple and blue, and much indurated. This change of 

 color and difference in degree of induration is due to their 

 closer proximity to the diabase sill in the Asbestos Canyon. 



The correspondence in lithographical character and vertical 

 succession of these two sections four miles apart is so close that 

 the individual strata of the sections can be matched bed for 

 bed. The only marked contrast in thickness occurs in the 

 basal white limestone (a). 



Third Member. — Argillaceous and Arenaceous /Shale. 



Section measured at East Wash in continuation" of the pre- 

 ceding section. 



a. Cliff-forming jasper. 



1. Dense, hard layer of blue-black jasper mottled 

 with red spots and showing no banding in the 

 mass, forming with the three following layers a 

 strong perpendicular cliff. This is the most 

 resistant rock in the Unkar. Where the under 

 surface shows beneath the overhang of the cliff 

 it is sun-cracked on a large scale and in several 

 generations „ 28' 



2. Same general character as 1, but showing a 

 banded structure. The lower 2 ft. are slaty and 

 weather out, giving the cliff an overhang 19' 



3. Same as 2 with a soft slaty layer at the base... 14' 



4. Same as 2 and 3 with a soft layer at the base. 12' 



Total 73' 



