506 Noble — Geology of the Grand Canyon, Arizona. 



Character Thickness 



b. Argillaceous a?id calcareous red shale and limestone. 



1. Soft, purple shale 6" 



2. Purple, cherty limestone ..„.. 1' 



3. Purple shale with occasional bands of purple 



calcite _ ... 4' 



4. Purple, crystalline limestone 1' 



5. Alternating layers of buff and chocolate-red 



shale with a splintery habit of weathering and 

 a roughly concretionary structure. Like all the 

 succeeding shales and sandstones of the TJnkar 

 they are mottled with light-colored spots which 

 are usually circular or elliptical in form and of 

 all sizes 5' 6" 



6. Blue limestone, white for \" at the base and 



showing dendritic markings 5" 



7. Redshale __•_. 1' 5" 



8. Blue limestone 4" 



9. Red shale ._ _ 3' 10" 



10. Purple limestone __ 6" 



11. Calcareous, red shale with three thin bands of 



purple limestone 9' 10" 



1 2. Red, crystalline limestone 1' 



13. Redshale. ._ 1' 



14. Red, crystalline limestone 1' 



15. Red shale ._ 11' 



16. Blue limestone 3" 



11. Redshale _• . - 1' 



18. Blue limestone 2" 



19. Pink limestone 1' 



20. Red shale 4' 4" 



21. Cherty, white limestone __ 4" 



22. Compact, red shale forming a cliff __ 8' 



23. Alternating layers of buff and red shale 13' 6" 



24. Dense, purple, calcareous shale carrying bands 

 of pink calcite and forming a cliff. Contains 

 occasional thin bands of chert ._ 9' Q" 



25. Blue, calcareous shale with an onion-like concre- 

 tionary structure on a large scale 5' 



Total 85' b n 



c. White limestone. 



1. Thin-bedded, white, cherty limestone carrying 

 the chert in parallel bands, and containing three 

 paper-thin layers of purple shale. Weathers 

 to a white powder. Dendritic markings are 

 present __ _ 2' 



2. Nodular, white, cherty limestone. The chert is 



present in irregular nodules of no definite shape. 



