Schuchert — Carboniferous of Grand Canyon of Arizona. 351 



sandstone reached by the writer while in the field is that 

 it represents the material of a large delta of continental 

 deposits laid down under constant but probably local 

 sheets of water that were evidently entirely fresh. The 

 Coconino may be the deposits of dune sands swept from 

 the north into a series of basins or fresh-water lakes like 

 the present fresh- and brackish-water lakes on the outer 



Fig. 2. 



Fig. 2. Contact of Coconino sandstone and red shales of Upper Supai, as 

 seen on Bright Angel trail. Note the sharp contact, foresetting lines of Coco- 

 nino, and sand-filled fissure in Upper Supai. 



borders of the Nile delta. (For further discussion of 

 this formation, see Noble, op. cit., p. 85.) 



That the Coconino sandstone invaded to the southward 

 a land -composed of the Supai formation is shown not 

 only in the very different nature of these underlying- 

 strata and the sharp contact between them, but especially 

 in the fact that the surface of the Supai has many verti- 

 cal solution joints now filled with the Coconino sands. 

 These filled fissures, up to 4 inches wide and 10 feet high, 

 are especially well seen on the Bright Angel trail, and a 

 photograph here reproduced (fig. 2) shows what they 



