UNKAR SECTION 217 



Feet Feet 

 i. This flow rarely forms a cliff, and the rocks crumble into a 



rather light olive-green coarse sand ; thin beds of reddish 



brown sandstone occur in several places 250 



• 800 



3. Sandstones (upper) : 



a. Shaly vermilion sandstones, with intercalated bands of a 



greenish gray,' followed below by 700 feet of vermilion beds 



of a uniform character 1,730 



b. The vermilion sandstones of " a " pass into chocolate-colored 



sandstones underlain by 300 feet of friable sandstone and 

 arenaceous and micaceous shale . 1,500 



Sandstones (lower) : 



a. Compact quartzitic gray sandrock, 25 feet, with 65 feet of 



hard, compact sandstone 90 



b. Massive, compact, cliff-forming, brown, buff, and purplish- 



brown sandstone 1,200 



c. Reddish brown to vermilion, friable, shaly sandstone, with 



fine, silicious conglomerate (10 feet) at the base 830 



,230 



2,120 



5. Alternating beds of sandstone and limestone 69 



6. Dark, compact basaltic lava in one massive, probably intrusive, flow. . 80 



7. Light gray, compact, shaly limestone, with pinkish tinge between the 



laminae 26 



8. Silicious conglomerate, formed largely of pebbles derived from the 



upturned edges of the pre-Unkar strata, upon which it rests uncon- 

 formably , 30 



Total tliickness of Unkar terrane 6,830 



Total thickness of Chuar terrane 5,120 



Total thickness of Grand Canyon series 11,950 



AGE OF CAMBRIAN BEDS RESTING ON GRAND CANYON SERIES 



The fauna of the sandstones and shales at the summit of the Tonto 

 sandstone, 290 feet above its base, is of middle Cambrian age and is of 

 the same type as that of the shales of the Flathead formation above the 

 Belt terrane, in Montana. 



The Cambrian Tonto sandstone is essentially a beach deposit, and 

 many of its beds are similar to those of the Flathead sandstone. 



The absence of the lower Cambrian rocks and fauna is attributed to 

 the fact that the portion of the continent now covered by the Grand 

 Canyon formations and the associated Cambrian rocks was a land sur- 

 face during lower Cambrian time. 



UNCONFORBIITY BETWEEN GRAND CANYON SERIES AND CAMBRIAN 



Location of the contact. — The contact of the Tonto Cambrian sandstone 

 with the rocks of the Chuar terrane is beautifully shown in the walls of 



