424 H. E. Gregory — Shinarump Conglomerate. 



Art. XXXY. — The Shinarump Conglomerate •* by H. E. 



Gregory. 



Extent and Topographic Expression. 



The conglomerate capping the Shinarump cliffs on the 

 extreme northern border of Arizona is represented by expo- 

 sures on the Navajo reservation and at other points south and 

 east of the Colorado Canyon. It constitutes a stratum some- 

 what unusual in character and extent, and has accordingly 

 attracted the attention of all geologists who have visited the 

 Plateau Province. Howell, f who traced these beds more or 

 less continuously from the Utah plateaus across Arizona and 

 New Mexico, speaks of this stratum as " one hundred feet thick 

 at St. George, forty or fifty feet to the east," and " coextensive 

 with the Triassic of the Colorado Plateau." Gilbert J remarks 

 that " its persistence over large areas is . . . such as to 

 excite wonder." Dutton expresses in even stronger terms what 

 was apparently the belief of all field workers associated with 

 Powell. In speaking of the Shinarump, including, however, 

 not only the conglomerate but also the beds below, the follow- 

 ing language is used : 



" Resting everywhere upon the Carboniferous of the Plateau 

 country is a series of sandy shales, which in some respects are the 

 most extraordinary group of strata in the West, and perhaps the 

 most extraordinary in the world. . . . There are especially 

 three characteristics, either one of which would render them in 

 the highest degree conspicuous, curious, and entertaining. 



" First may be mentioned the constancy with which the com- 

 ponent members of the series preserve their characters through the 

 entire province. • Wherever their proper horizon is exposed they 

 are always disclosed, and the same well-known features are pre- 

 sented in southwestern Utah, in central Utah, around the junction 

 of the Grand and the Green, in the San Rafael Swell, and at the 

 base of the Uinta Mountains. As we pass from one of these 

 localities to another, not a line seems to have disappeared, not a 

 color to have deepened or paled. . . . The constancy is, so 

 far as known to me, without a parallel in any formation in any 

 other region." § 



My own wanderings in the Plateau Province, dating from 

 1900, lead me to assent in general to the views expressed by 

 the group of geologists who introduced the canyon land to the 



* Published by permission of the Director of the United States Geological 

 Survey. 



f Geological Surveys west of 100th Meridian, III, pp. 230-285. 



X Ibid. Pt. I, p. 175. 



§ Geology of the High Plateaus, p. 144. 



