I04 WHITMAN CROSS 



The Shinarump conglomerate is said to be within "the transitional 

 shales" of 550 to 750 feet thickness below the Vermilion Cliff sand- 

 stone — shales not described except as "monotonous." The con- 

 glomerate is said to "consist of fragments of silicified wood imbedded 

 in a matrix of sand and gravel." Its thickness rarely exceeds fifty 

 feet. "It occasionally thins out and disappears, but usually recurs if 

 the outcrops be traced onwards, resembling the mode of occurrence 

 common to the coal seams of the Carboniferous coal measures." It is 

 indeed suggested that the conditions under which the conglomerate 

 was accumulated "may have been similar to those attending the forma- 

 tion of coal." " The subsequent silicification of the wood " is regarded 

 as remarkable and no possibility that any part of the wood may 

 have been derived from earlier formations seems to have been enter- 

 tained (6, p. 147). 



Walcoti's section in the Kanab Valley. — In 1879, ^s his first 

 work in connection with the U. S. Geological Survey, C. D. Walcott 

 made a careful section of the formations displayed so well in 

 the Kanab Valley, from the lower Tertiary to the pre- Cambrian 

 of the Grand Canyon. As a result of this study, Walcott an- 

 nounced in 1880 the discovery of Permian fossils in the beds 

 between the Aubrey limestone and the Shinarump conglomerate, 

 i. e., the lower part of Powell's Shinarump Group (24). He 

 found a plane of unconformity by erosion above the Aubrey, 

 as stated by Powell, and another below the Shinarump con- 

 glomerate, as noted by Gilbert at other localities, and a third in 

 the intermediate beds. Permian fossils were found either side of 

 the last break. 



The unconformity below the Shinarump conglomerate was further 

 described some years later (25) on the basis of new observations, 

 but the full section of the Shinarump and superjacent formations was 

 first published in connection with a discussion of the western Colorado 

 red beds and their correlation, by myself (4, p. 484). For comparison 

 with Powell's section, also in the Kanab Valley, and that of Ward, 

 to be given later, it seems desirable to give the section made by Walcott 

 from the Aubrey to the Marine Jura. This I am able to do through 

 Mr. Walcott 's generosity and kindness in giving me unrestricted 

 use of his notes 



