FIUX'll.l 



SECTION IN CONGRESS CANYON. 



477 



ical divisions: Archean, Algonkian, Cambrian, and Carboniferous. The 

 more important divisions of these groups are marked by the Roman 

 numerals 1 to VII, ^ 



ih s- — — 



if.-. 



ifr. 



y~ 



iS 



K— 



in ascending or- 

 der, in Fig. 32. 



I . Archean. 

 Gneiss with intra 

 sive dikes of gran- 

 ite, pegmatite, and 

 later diabase. 



II. A Igow, k'mn. 

 Grand Canyon se- 

 ries,* lying uncoii- 

 formably on the 

 gneiss. Coarse 

 red sandstones, 

 shales, and con- 

 glomerates, with a 

 sheet of diabase in 

 the lower part (in- 

 trusive or surfaee 

 flowt). Its total 

 thickness, as ob- 

 served at other 

 points, is over 13,- 

 000 feet (4,000 in.); 

 in this section only 

 300 to 400 metres 

 are exposed. 



1 Hand IV. Cam- 

 brian, (about 1,000 

 feet (305 m.) thick 

 lying uneonform- 

 ably on the up- 

 turned edges oft he 

 Algonkian beds. 

 The faults which 

 traverse the latter F '«- 32.-s,.<-tin„ la Oangwea canyon. 



beds terminate at the base of the Cambrian. 



/ 



U:' 



*The Grand Canyon series is fully developed only in flic main canyon and thins out 

 Ib the smaller valley through which the trail from Hanee's oabin descends. The 

 Cambrian sandstone rests directly on the gneiss in the picturesque niche or panel ' M 

 called St. Gahriel's Cathedral (26 in. high), where the geologists camped the first 

 night. 



