Schuchert — Carboniferous of Grand Canyon of Arizona. 349 



of New Mexico. He also suggests that the Kaibab may 

 be equivalent to a part of the Guadalupian of south- 

 western Texas, a formation of undoubted Permian age. 



Coconino Sandstone. 

 The Coconino sandstone in the Bright Angel quad- 

 rangle is 385 feet in thickness and is a most persistent 

 formation for one of wholly sand accumulation and, fur- 

 ther, one which is nearly devoid of horizontal stratifica- 

 tion (see fig. 1). Its yellowish gray to creamy white 

 color is everywhere to be seen, even in the far distance as 

 a white band near the top of the canyon walls. In closer 

 view one notes that it is almost unbedded and composed 

 of foreset beds that have dips averaging between 20° and 

 25° to the south. Noble tells me the dips vary between 5° 

 and 30° (see fig. 2). These very long foresetting planes 

 so clearly shown on all the old weathered surfaces have 

 been noted by all geologists and are also shown in one of 

 Holmes 's wonderful drawings, plate 30 published in 1882 

 in Dutton's Tertiary History of the Grand Canyon Dis- 

 trict. Even though the Coconino formation steadily 

 thins to the north and northwest, the foresetting shows 

 that the sand was derived from that direction. To the 

 southward in the Aubrey Cliffs the thickness is given by 

 Gilbert as 700 feet. 4 In general the quartz sand is sharp 

 and of fine grain, but in limited bands the grains are con- 

 siderably larger, well rounded and with dull surfaces. 

 The latter kind is clearly wind-blown sand, and it should 

 be expected in near-shore deposits of Permian time 

 because of the then prevalent arid climates. The eolian 

 sand, it appears, has been blown into rivers that have 

 brought it from a long distance to the northward and 

 out of it in the course of transportation has been washed 

 or blown almost all other disintegrated rock material 

 than the quartz. As the Coconino formation stands up 

 in vertical cliffs, it probably has a cement of silica besides 

 the iron that gives it its slightly yellowish color, but the 

 quantity of cement appears to be very slight. Ripple- 

 marking is rare but was noted on both the Hermit and 

 Bright Angel trails. The troughs are very shallow, 

 probably less than 5 mm. deep, with the wave crests about 

 5 inches apart. From time to time, after 50 to 100 feet 



4 G. K. Gilbert, U. S. Geol. Survey W. 100th Merid., vol. 3, pt. 1, p. 82, 

 1875. 



