478 GEOLOGICAL EXCURSION TO THE ROCKY MOUNTAINS. 



The Cambrian is subdivided into — 



III. Loircr Tonto, (about 300 feet) massive red sandstones with Scoli- 

 tlius at the top. 



IV. Upper Tonto, (about 475 feet) greenish shales and shaly sand 

 stones with impure limestones in the upper part. 



The Devonian, which has been observed by Walcott 95 on the 

 other side of the Grand canyon, between Marble canyon and Kaibab 

 plateau, is altogether wanting at this point. The unconformity of 

 erosion at the base of the Red Wall limestone, observed by the same 

 geologist, is also yery obscure here. There seems to he a gradual pas- 

 sage from the arenaceous sediments of the Tonto to the Carboniferous 

 limestones above, but the fact that a sandstone bed is intercalated at 

 the base of the Carboniferous limestones is consistent with Walcott's 

 observations. 



V. Lower Carboniferous, aa,. 1,000 feet. Red Wall limestone. 



(a) At the base: alternating - sandstone and limestone. 



(b) Red and white stratified (thin-bedded I) limestone, in part eri- 

 noidal limestone with easts of Splri/crstriatus. 



(c) J>ed of bluish breeciated limestone. 



Above these comes the cliff of the l\vd Wall; it consists of a massive 

 or obscurely bedded pure white limestone, which is superficially colored 

 by waters seeping through the red beds of the Aubrey group. 



VI and VII. Upper Carboniferous or Aubrey group. 



VI (a). Lower Aubrey sandstone and shale, ca. 1,000 feet. The upper 

 and lower parts are formed by thin-bedded sandstones and shales; in 

 the middle there is a well defined cliff of massive sandstones. 



VI (/>). White Aubrey sandstone, ca. 100 feet, cross-bedded and 

 forming a steep cliff distinctly visible from a long distance as a white 

 band in the midst of the red rocks. 



VII. Aubrey limestone and dolomite, ca. 500 feet (800 feet on 

 the other side of the canyon). In the lower part is found a pure lime- 

 stone which rests directly on the sandstone without any transition. 

 The upper part consists of cherty limestones which contain a large 

 Allorisma and some ill-preserved gasteropoda {EuomphaluB and Pleuro- 

 tomariu). [n Coconino or Walnut canyon, near Flagstaff, the follow- 

 ing Brachiopoda were found in the faint pink-colored dolomite in which 

 are thefamous cliff dwellings. (See p. 475.) 



Productus Tvesii, Newberry, very common. 



Productus all'., scdbriculus, rare. 



fipirifer (Martinia) lineata, Marsh, rare. 



Thespeeimens of P. Ivesii are very clearly related to the Upper Car- 



