112 WHITMAN CROSS 



observation not to be found in Ward's papers. It is plain that 

 Powell applied the name to a particular conglomerate seldom found 

 to exceed more than one hundred feet in thickness and that all other 

 writers I have cited, with the exception of Ward, have used the 

 term for what they believed to be the same conglomerate. It appears 

 to be impossible to locate the actual horizon of the Shinarump con- 

 glomerate in the Shinarump formation of Ward, yet, as the ensuing 

 discussion will show, it is particularly important to ascertain the 

 relation of the beds containing the reptilian fauna discovered by 

 Ward to the Shinarump conglomerate of earlier investigators. 



For reasons to be developed, it appears to me not improbable that 

 the horizon of the Shinarump conglomerate proper is near the beds 

 in which the vertebrate fossils were found, possibly at the base of the 

 Leroux member of Ward. The statements of Powell and Dutton 

 indicate that the conglomerate may become inconspicuous through 

 thinning and that it may locally disappear as a conglomerate. Its 

 horizon may be difficult of detection where the conglomerate phase 

 is absent. 



If it be assumed for the moment that the eight hundred feet of 

 beds designated by Ward the Lithodendron member are below the 

 horizon of the Shinarump conglomerate proper, there is reason to 

 believe that those eight hundred feet of strata belong in truth with 

 the Moencopie beds, the transition reported by Ward in Red Butte 

 having the significance suggested for it by him. On this same 

 assumption the Leroux beds of Ward fall into place as the lower 

 Triassic of the Little Colorado Valley. 



No fossils surely belonging to the Moencopie formation were 

 found by Ward. Fossil wood is common in both members of the 

 Shinarump. The celebrated "petrified forest" in which large pros- 

 trate silicified trunks are abundant represents more than one 

 stratigraphic horizon. The so-called "upper" and "lower" forests 

 are said to be in the Lithodendron beds, while the "middle" forest 

 is in the Leroux member. As but one species of the silicified wood 

 has been identified this abundant material is of little diagnostic value at 

 present. The single species studied is Araucarioxylon arizonicum 

 Knowlton (15), based on two fossil trunks collected by Lieutenant 

 Hegewald, in 1879, of which the horizon of occurrence is unknown. 



