CORRELATION OF FORMATIONS 479 



In some places the bedding is inconspicuous and several hundred feet 

 of sandstone may appear as one unit of massive rock. Cross-bedding is 

 often very pronounced, as in the striking remnant of erosion called the 

 u Navajo church." The lower portion is the more massive, the upper 

 part more friable, and gypsiferous shales are common in the latter. 

 Above the Zuni sandstones comes the Cretaceous section, beginning with 

 the undoubted equivalent of the Dakota. 



Comparing the formations of the Zuni plateau, as described by Dutton, 

 with those of southwestern Colorado, it seems probable that the Zuni 

 sandstones represent the Gunnison group. Dutton's section is not suffi- 

 cienly detailed to permit a suggestion as to the exact equivalents of the 

 La Plata and McElmo formations, but it is difficult for me to suppose 

 that the Navajo church is constituted of anything but one of the La 

 Plata sandstone members. 



The Wingate sandstone corresponds in position and character to the 

 upper, vermilion-colored sandstone of the Dolores formation. The ab- 

 sence or subordination of cross-bedding and the constancy of the red 

 color both tend to support such a correlation. If the Wingate is upper 

 Dolores, it would appear probable that the " lower Triassic " of Dutton 

 is at least approximately the equivalent of the lower Dolores, and it may 

 well be that the basal conglomerate called the Shinarump by Dutton is 

 actually the same as the basal conglomerate of the Dolores. Dutton 

 does not speak of limestone conglomerates in the Trias, nor did he find 

 fossil remains in it, except the abundant fossil wood. 



If the Wingate sandstone belongs to the Dolores, Dutton was probably 

 wrong in saying that the striking towers and pinnacles of the lower San 

 Juan valley are made of that sandstone, for the observations of Gane 

 indicate that the lower La Plata sandstone is the one producing the 

 prominent erosion forms of the San Juan, being there of pronounced red 

 color. 



Beneath the Trias in the Zuni district is Dutton's Permian, lithologic- 

 ally atypical Red bed formation. That would correspond to the Cutler 

 formation in stratigraphic position ; but other factors enter into the prob- 

 lem at this point and render any definite suggestion of such a correlation 

 premature. Below the Zuni Permian comes the Aubrey group, and 

 beneath the Cutler occurs the Hermosa formation (ignoring the uncer- 

 tain Rico beds), both Aubrey and Hermosa carrying Pennsylvanian 

 invertebrate faunas. Dr G. H. Girty informs me, however, that these 

 faunas are not known to have a single species in common, and the equiva- 

 lence of the two fossiliferous formations is therefore by no means to be 

 assumed, though their stratigraphic position seems to be the same. It 

 is hoped that data bearing on this question may be obtained in the near 



LXIII— Bull. Gkol. Soc. Am., Vol. 16. 1904 



