II. E. Gregory — Shinarump Conglomerate. 431 



below, was originally assigned by Powell to the lower Triassic. 



" This escarpment is capped by a firmly cemented conglomerate 

 containing many fragments of silicified wood, and over its sur- 

 face are scattered many like fragments, and sometimes huge tree 

 trunks, which are the remnants of rock at one time overlying the 

 conglomerate, but now carried away by erosion. Underlying 

 this cap are variegated sandstones and marls. The whole group 

 is probably of lower Triassic age." * 



Walcott (1879) placed the Shinarump conglomerate definitely 

 at the base of the Triassic overlying the Permian, a determina- 

 tion used by Dutton in his Grand Canyon and Zuni reports. 

 Since the publication of Button's classics, the stratigraphy of 

 the region containing these beds has been studied by Ward 

 (1900-01), by Woodruff (1910), and by the writer (1909-11). 

 Important data, chiefly geographical, but also of indirect strati- 

 graphic value, especially for the region north of the Canyon, 

 was obtained by Davis, f by Johnson, \ and by Huntington and 

 Goldthwait.§ 



Ward concluded that not only the Shinarump conglomerate, 

 but a large part (at least 700 feet) of the underlying shales 

 (Moencopie) are of Triassic age. " Certain geologists hold that 

 the series of beds which I have included under the name of 

 Moencopie belong to a different system [from Shinarump] and 

 is in some way connected with the underlying Paleozoic rocks. 

 This view ... is, in my opinion, quite untenable."] This 

 grouping of part of the Moencopie with the Shinarump con- 

 glomerate and ascribing them both to the Triassic is an inter- 

 pretation quite at variance with that expressed by other 

 workers in these fields, unless the descriptions of Xewberry, 

 Marcou and Blake may be so interpreted. The chief difficulty 

 arises from the fact that with the exception of a few indeter- 

 minate bone fragments found by the writer at Oljato no 

 fossils have been collected from the Shinarump conglomerate. 

 Its age is, therefore, to be determined by a study of its relations 

 to the subjacent and superjacent beds, whose position in the 

 time scale is fairly well known. The evidence thus derived is 

 reasonably satisfactory and the conclusions drawn may, for the 

 sake of clearness in presentation, be stated at this point : The 

 Shinarump conglomerate marks the base of the Triassic of the 

 Plateau Province. It is separated from the underlying shales 



* This Journal, vol. v, pp. 457-458, 1873. 



f Excursion to the Grand Canyon of the Colorado, Bull. Mus. Comp. Zool., 

 Harv. Coll., xxxviii, No. 5, 1901; Excursion to the Plateau Province of 

 Utah and Arizona, ibid., xlii, 1903. 



{Proc. Boston Nat, Hist. Soc, xxxiv, 1909, pp. 135-161. 



§ Hurricane Fault in Toquerville District Utah, Bull. Mus. Comp. Zool., 

 xlii, 1904, Geol. Ser. vi, No. 5. 



|| U. S. Geol. Sur., Monograph XLVIII, p. 22. 



