H. E. Gregory — Shinarump Conglomerate. 



433 



Last Bluff and southwest (Howell) 



(Geog. Surv. West of 100th meridian, 

 iii, pp. 271-272, 1875) 



Variegated gypsiferous marls 400' 



Shinarump conglomerate containing 

 silicified wood 



Gray conglomerate with large quan- 

 tities of petrified wood 50' 



[Unconformity not noted] 



Chocolate, arenaceous and gypsiferous 

 shales and marls. 



Red, sandy shale and massive, tan 

 sandstones (Moencopie) 1260' 



Oljato (Gregory) 



Shales and limestone of Dolores 



formation 

 Gray grit to conglomerate, quartz 



pebbles and fossil wood. 35' 



Unconformity 



Argillaceous gray shales 3, 



Chocolate-red, thin sandy shales 35 



Nashlina (Gregory) 



Variegated and shales with limestone 



conglomerate 100' + 



Gray grits and conglomerate and 



wood 40' 



Unconformity 

 Chocolate sandstone 100' -h 



Gypsum Valley (Woodruff) 



(Bull. 471, U. S. Geol. Surv., pp. 82- 



85, 1910) 

 Sandy variegated shales (Dolores) 



1330' 

 Massive brown, gritty, cross-bedded 



sandstone (Oljato) 380' 



Unconformity ? 



The conclusion stated above and illustrated by the sections 

 given, rests on the following facts of field observation : (1) con- 

 tinuity, lithologic similarity and equivalent age of the beds 

 below the Shinarump conglomerate, (2) equivalence of beds 

 above that datum, and (3) the presence of a widely extended 

 unconformity. 



(1) As to the nature and relations of the strata above the 

 Shinarump conglomerate, there is substantial agreement, 

 although inconclusive evidence of unconformity above this bed 

 was noted by Woodruff* on the San Juan Kiver, Utah, and 

 by the writer in the Black Creek valley, Arizona. Everywhere 

 these beds are shales and marls with layers of limestone and 

 varying amounts of sandstone prevailingly calcareous. The 

 limestone, usually a conglomerate, possesses such individuality 

 that lithologic equivalence might be postulated on the evidence 

 of this feature alone, and it is not surprising that this forma- 

 tion (Dolores of Cross; Leroux, in part, of Ward, " variegated 

 shales " of other writers) should be described in terms which 

 apply equally well to such widely separated areas as the 

 La Plata mountains, Colorado, the Moencopie valley, Arizona, 

 Leroux Wash, Arizona, and Fort Wingate, New Mexico 

 In the course of my work in the Navajo country, opportunity 

 has been afforded to trace these beds with inconsiderable inter- 

 ruptions from the Dolores River, Colorado, to Holbrook, 

 Arizona, and from Echo Cliffs, Arizona, to Navajo Church, 

 New Mexico, an experience which leaves no doubt in my mind 

 that at all points the same formation is present. 



* Woodruff : Geology of the San Juan Oil Field, U. S. Geol. Surv., Bul- 

 letin No. 471, Part II, p. 83, 1910. 



Am. Jour. Sci.— Fourth Series, Vol. XXXV, No. 208.— April, 1913. 

 30 



