150 ENVIRONMENT OF VERTEBRATE LIFE, ETC. 



" In its stratigraphic position the Cutler formation of the San Juan Mountains 

 corresponds to the Mpenkopi formation, and the two are lithologically somewhat 

 similar." 



The De Chelly sandstone. A massive, cross-bedded sandstone peculiar 

 to the Navajo Country is named by Gregory the De Chelly sandstone. 

 This had previously been correlated with the Vermillion Cliffs or the Wingate 

 sandstone. 



(Page 32.) "Section of De Chelly sandstone at west entrance of Bonito Canyon, near Fort Defiance. 



"[Measured by K. C. Heald. Dip, 16 E.] 



"Shinarump conglomerate. 



"Unconformity. Feet. 



1. Sandstone, light red, fine-grained; clear- white and red rounded quartz grains; calcareous and 



ferritic cement; contains rare pebbles one sixty-fourth to one-sixteenth inch in diameter; 

 massive, cross-bedded in places; weathers into rounded knobs; in two beds, 13 and 15 feet 

 thick 28 



2. Sandstone, tan to brown, fine-grained; clear, well-rounded quartz; calcareous cement; many 



specks of limonite; even-bedded to slightly cross-bedded; hard; forms nearly vertical cliff; 



in three beds, 7,3, and 6 feet thick 1 6 



3. Sandstone, chocolate-colored to gray-brown, fine to medium grained; clear, well-rounded quartz; 



massive; parts of the bed show no structure; other parts cross-bedded with curved laminae 

 tangential to a horizontal surface; weathers in rounded bosses 77 



4. Sandstone, chocolate-colored, shaly, largely concealed by talus 27 



5. Sandstone, light red, fine-grained; clear to red rounded quartz grains; bottom 5 feet thin-bedded; 



in the center gray, cross-bedded, resistant sheet, ij feet thick; remainder massive, incon- 

 spicuously cross-bedded 115 



Moenkopi shales. 



263 



This section is characteristic of the De Chelly sandstone in a general 

 way wherever it occurs. It is mentioned as occurring at Defiance Hogback, 

 Buell Park, lower Black Creek, Canyon De Chelly, San Juan Valley in 

 Utah, Monument Valley, etc. 



(Page 33.) "Structure, texture, and composition [of De Chelly sandstone]: 



"With the exception of the Navajo and Wingate sandstones, which it resem- 

 bles in many physical features, the De Chelly sandstone presents the most 

 massive strata of all the red beds. In the wall of Canyon Bonito beds 5 to 10 

 feet thick are found near the top; but in the same locality 60 to 70 feet of strata 

 with most obscure bedding stand vertically in the wall. At Oljeto a single bed 

 is 85 feet thick, and in Canyon del Muerto and Canyon De Chelly there are 

 massive beds 200 to 300 feet thick, with no definite planes of separation. Here 

 and in Monument Valley giant slabs of rocks splitting off from the massive beds 

 leave clean, smooth faces hundreds of square feet in area, marked only by the 

 delicate tracery of cross-bedding laminae. 



"The De Chelly sandstone is fine-grained throughout and remarkably uniform 

 in texture. It consists essentially of grains of two sizes spherical grains of 

 quartz, averaging about 0.19 mm. in diameter and making up the bulk of the 

 rock, and less well-rounded grains 0.5 to 0.6 mm. in diameter. In places grains 

 of the two sizes are intermingled, but commonly the larger grains are sprinkled 

 over the surfaces of cross-bedding laminae. Here and there slightly larger grains 

 are found as lenses or strings marking cross-bedding division planes, and rarely 

 scattered pebbles one-sixteenth to one-eighth inch in diameter are seen. White 

 rounded quartz grains constitute about 95 per cent of the rock; red and amber 



