CORRELATION OF FORMATIONS 483 



canyon and can be traced for hundreds of miles with scarcely a break. 

 These terms are also used by Gilbert and Dutton, save that they substi- 

 tute the name Gray Cliff for White Cliff. 



The reconnaissance explorers of this vast labyrinth of canyon, scarp, 

 and terrace necessarily strove to grasp first the major elements of the 

 problems before them, and it seems clear that in their broader correla- 

 tions they were in the main correct. The great cliff-makers, the Ver- 

 milion and the White Cliff or Gray Cliff sandstones, are traced by Powell 

 to northern Utah and the adjacent portion of Colorado (36), and by 

 Dutton across the Grand canyon to the Echo cliffs above the section 

 examined by Ward. But eastward, toward the San Juan mountains, the 

 change in character of these sandstones caused Dutton to hesitate. He 

 indeed says distinctly that " the Jurassic White sandstone (White Cliff) 

 seems to be peculiar to the northern and western portions of the Plateau 

 province. In southern Colorado and western New Mexico no strati- 

 graphic member has yet been found which can be identified with it "(8). 

 But this positive statement is at once followed by the suggestion, now 

 known to be correct, that through a thinning and assumption of red 

 color, the Jurassic in this eastern district may be wrongly assigned to the 

 Triassic, together with the also diminished Vermilion cliff (8). It seems 

 peculiar, however, that in the report on the Zuni plateau (10) Dutton 

 did not recognize that the white cross-bedded strata of the Navajo church 

 might be the representative of the White Cliff sandstone. It will be 

 recalled that he did correlate the underlying Wingate sandstone with the 

 Vermilion cliff. 



The great cliff-forming sandstones of the Plateau province are of sim- 

 ilar texture and not yet greatly indurated. They seem to grade one into 

 the other at many points, and the line between them is generally arbi- 

 trary as drawn by Powell, Dutton, and others. Powell, indeed, includes 

 the White Cliff in the Triassic because of the apparent transition below 

 and the sharp line above, where a limestone bearing a marine Jurassic 

 fauna appears. But this seeming gradation also appears in Colorado, 

 where it is perfectly plain that a part of the Dolores sandstone has been 

 removed, and near localities where the magnitude of the stratigraphic 

 break between these formations is very evident. The soft Dolores sand- 

 stones were no doubt broken up and redeposited. forming a large part 

 of the lowest La Plata beds and causing the apparent transition. 



Observations by C. D. Walcott. — The general observations of Powell, 

 Dutton, and Gilbert concerning the Plateau formations were supple- 

 mented by Walcott in 1879 through detailed studies of the excellent 

 section displayed in the Kanab valley, and again in 1882 by special 

 examination of the Paleozoic formations. A portion of the results ob- 



