3G0 Seltiir/t, /■/ — Carboniferous of Grand Canyon of Arizona. 



lobus, Pugnax utah, Lophophyllwn i)rofundum,Fusulina, 

 etc., etc. From this we see that here the waters were 

 more normally marine than in the area of the Grand 

 Canyon. 



Redwall Limestone. 



The Redwall limestone beneath the Supai has a thick- 

 ness of 550 feet and makes the most precipitous cliffs 

 in this dry climate of the Grand Canyon. To the west 

 the formation thickens and in the western part of the 

 Shinumo quadrangle it is 700 feet thick. It consists of 

 heavy-bedded, dense, hard and brittle limestone, with 

 dolomites and sandstones toward the base. On fresh 

 fracture, the limestones have in general a bluish gray or 

 yellowish gray color. There are no shale partings and 

 the Redwall therefore appears as one unbedded mass. 

 Noble says, in the Bright Angel topographic sheet: 13 

 "Its face is recessed by niches and alcoves and is stained 

 red by the wash from the Supai strata above." It is 

 also much pitted through weathering and cuts fingers 

 and clothing. Redwall is therefore a misnomer for this 

 formation, which is the most difficult one of all in the 

 Grand Canyon to understand from the historical stand- 

 point. The overwash hides the very nature of the strata 

 and the few fossils it has. These latter are casts of fos- 

 sils in dolomites, occasionally an actual one in dense lime- 

 stones that one can not get, and where there is chert 

 they are poor siliceous pseudomorphs. The diagenetic 

 changes and the dense limestone nature of the formation 

 have apparently obliterated what organisms there may 

 have been originally. To the south and southeast the 

 Redwall becomes somewhat thinner bedded and intro- 

 duces some shale and sandstone. 



The base of the Redwall on the Hermit trail consists 

 of three thick beds. The upper one is from 10 to 12 feet 

 thick, and the lowest bed is 8 feet thick, of a vesicular 

 gray dolomite with the cavities filled with calcite. The 

 upper bed has Syringopora cf. surcularia. Between 

 these two dolomite beds is a yellowish white sandstone, 4 

 feet thick. 



The Redwall may be studied on the Hermit trail below 

 the ' ' Cathedral Stairs ' ' but the sequence can not be made 

 out with certainty because all of it has slumped and slid 

 down in a huge landslide. The parts are mixed and even 



13 Noble, TJ. S. Geol. Survey, Bright Angel Topographic sheet, 1914. 



