■Ii6 WHITMAN CROSS 



Beneath this section comes the Aubrey sandstone; above it is 

 the VermiHon ClilT sandstone. 



This section is materially different from those given by Powell, 

 Walcott, and Ward, but no explanation is offered by Gilbert. He 

 states that evidence of unconformity below the Shinarump conglom- 

 erate was not found in the Henry Mountains, but if only four hundred 

 feet of strata there intervenes between the conglomerate and the 

 fossiliferous Aubrey, there is reason to believe that the stratigraphic 

 break at that horizon is considerable. 



The constitution of the beds assigned to the Shinarump is certainly 

 different from that of the typical section of the Kanab. There is 

 nothing said of sandstones on the one hand or gypsiferous beds on 

 the other. 



The Lower San Juan Valley. — In connection with this Henry 

 Mountains section, it is well to consider the observations made by 

 H. S. Gane on the northern side of San Juan River, near the Colorado, 

 which I made public in an earlier discussion of the red beds of the 

 Plateau Province (4, p. 476). Gane traced several Mesozoic forma- 

 tions down the San Juan Valley from the head of McElmo Creek in 

 Colorado, a point very near the La Plata quadrangle, where he had 

 assisted in the study and mapping of those formations, under my 

 direction1(2). Among the formations, the continuity of which 

 to the Colorado Canyon seemed clear to Gane, is the Dolores Triassic 

 formation, at the base of which and recurring irregularly in the lower 

 sandstone is a fine-graided conglomerate consisting largely of lime- 

 stone pebbles and carrying teeth and fragments of bones of several 

 vertebrates. Tracing this fossiliferous zone down the valley, Gane 

 found in it at Clay Hill divide, about twenty miles east of the northern 

 end of Glen Canyon, a portion of a crocodile jaw, unusually well 

 preserved. This specimen was described by Lucas (16) as the 

 type of Heterodentosuchus ganei. This form is the most abundant 

 one in the collection made by Ward and Brown in the Leroux beds 

 and it is also very common in the Dolores formation in the San Juan 

 region of Colorado, as appears from the work in my charge. Unios 

 were noted by Gane associated with the vertebrate. 



There is no means of proving that the conglomerate called the 

 Shinarump by Gilbert in his section is the same as that carrying 



