THE 



JOURNAL OF GEOLOGY 



FEBRUARY-MARCH, igo8 



THE TRIASSIC PORTION OF THE SHINARUMP GROUP, 



POWELL 



WHITMAN CROSS I 



Introduction. — ^Among the great sedimentary formations or groups 

 of the Plateau Province, described by Powell, Button, Gilbert, and 

 others, that one named by Powell the Shinarump is today the least 

 known and occasions the greatest difficulty in correlation. As I 

 have recently attempted to correlate the formations of the Plateau 

 Province with those of the adjoining mountain district of southwestern 

 Colorado, the difficulties in regard to the Shinarump have come 

 prominently to my attention, and it is hoped that a brief review of the 

 subject may be of material assistance to geologists who attack the 

 problem in future. 



The Shinarump is the lowest of three formations or groups assigned 

 by Powell to the Trias, the others being the intermediate Vermilion 

 Cliff sandstone and the White Cliff sandstone at the top. The 

 Triassic was thus supposed by him to embrace everything present 

 in the great section north of the Grand Canyon between the upper 

 Aubrey (Pennsylvanian) and the marine Jurassic. 



Button and other writers have referred the White Cliff sandstone 

 to the Jurassic, and this reference is no doubt correct, since the con- 

 tinuity has been established between this very well-marked formation 

 and the La Plata sandstone of Colorado, which is in angular uncon- 

 formity with the Triassic and the entire Paleozoic section (4).^ The 



1 Published with the permission of the Director of the U. S. Geological Survey. 



2 Numbers in parentheses refer to the bibliographic list to be found at the end 

 of this paper. 



Vol. XVI, No. 2 97 



