438 H. E. Gregory — Shinamtmp Conglomerate. 



capped by the Shinarump conglomerate. However, as regards 

 the vertical extent of the Permian beds, I am unable to assent 

 to the conclusion of Ward, who considered it " very probable 

 that the lower portion of the Moencopie beds belongs to the 

 Permian." * In the absence of evidence to the contrary, it 

 appears to me better to assign all strata between the " Upper 

 Aubrey" (Kaibab limestone) and the Shinarump conglomerate 

 to the Permian. This conclusion is in harmony with Walcott's 

 studies and with the views of Cross and coincides with the 

 results obtained by tracing of outcrops southeastward from 

 the month of the Little Colorado. 



In the discussion of the stratigraphy in the San Juan Oil 

 Field, f the Oljato sandstone member is ascribed, with consider- 

 able hesitation, by Woodruff, to the Permian. This was done 

 after a conference with the present writer, and quite with my 

 approval. While we both recognize the distinctive character 

 of this bed, yet it seemed " out of placed and on the whole 

 it was thought best to treat it as the upper member of the sand- 

 stones which form such a prominent part of the lower " Ped 

 Beds" along the San Juan. Massive tan sandstones underlie 

 the Oljato and the evidence of unconformity is not at all clear. 

 Later field studies have led me to the belief that the Oljato 

 sandstone member may be wholly or in part the Shinarump con- 

 glomerate, — an interpretation which does not conflict with the 

 field evidence and is entirely in agreement with the interpre- 

 tation of the stratigraphy of the Plateau country as a whole. 



Conclusion. 



The extension of field work over the previously unexplored area 

 between the San Juan Piver and the Santa Fe railroad and east 

 of the Little Colorado River reveals the fact that the Shinarump 

 conglomerate of Powell is practically coextensive with the 

 province ; that it occupies the base of the Triassic and serves 

 as a datum plane for stratigraphic work in this area ; that the 

 strata below are Permian, and that the strata above are Upper 

 Triassic ; that the conglomerate itself is Triassic, but whether 

 Upper. Triassic or older is undetermined. 



Yale University. 



*U. S. Geol. Surv., Monograph XLVIII, p. 19. 

 fU. S. Geol. Snrv., Bulletin 471, Pt. II, p. 83, 1910. 



