PEALE.] GEOLOGY DAKOTA GROUP GUNNISON RIVER. 131 



side of the Gunnison at various points between the mouth of Cochetopa 

 Creek and the mouth of Lake Fork. 



The drainage had probably then the same general direction it has at 

 present. In Fig. 2, Plate VII, beneath station 77, at the point d, we have 

 on top of the Dakota group a few shales. Farther north, at station 79, 

 there is greater thickness, reaching in all probability as high as No. 4. 

 The wearing down was probably from north toward the south, which is 

 the general direction of the streams at present. 



The following section was made from the point a to &, in Fig. 1, Plate 

 XIV. 



Jfo. 11. — Section of No. 1 Ct^etaceous, beneath station 73 north side of Gun- 

 nison River. 



Base. • Thickness in feet. 



1. Dark micaceous gneiss 



a-2. Siliceous saudstone, general color yellowish, becoming pink and white in 



places. The lower portion is somewhat concealed in beds that are massive. 43 



3. Siliceous sandstones like those of No. 2, general color pink. These sandstones 



are not so massive as those of No. 2. They are somewhat laminated 58 



4. Yellow sandstones in bands of two and three feet thickness 32 



5. Sandstones and interlauiinated shales. The general color of the sandstones is 



yellowish ; some of the layers have greenish pebbles. The shales near the top 

 are greenish 79 



6. Laminated brownish-gray sandstones in bauds from a foot to eighteen iuches 



in thickness. There are greenish-gray interlaminated shales. Some of Ihe 

 sandstones are probably argillaceous and weather into rounded bowlder-like 

 masses 6 



7. Space lilled with bandsofsandstoneandsoftargiilaceousshales and limestones. 



In the lower part there is a nodular limestone with pebbles of red jasper. 

 The upper parts of the sandstones are faintly tinged with purple 82 



8. Greenish and yellowish indurated argillaceous sandstones and shales, resem- 



bling the beds of No. 7 52 



9. Soft yellow and white laminated sandstones 16 



10. Soit pinkish laminated sandstones 14 



IL White argillaceous sandstones and shales; some of the beds are indurated and 



break with a conchoidal fracture. The sandstones weather with rounded 



corners, forming bowlder-like masses as in the case of No. 6 54 



12. Massive yellow siliceous sandstones, about - 100 



Top. 



Total, about *. 5:^6 



These sandstones and shales are exposed on both sides of the river 

 beneath the breccia, and also for some distance up the lateral branches. 



is^orth of the Grand OaQon the gently-sloping surface between the 

 Gunnison and Smith's Fork is underlaid by the Dakota group, which 

 forms a bluff-like edge above the granitic shelf bordering the caiion. 

 The slope is about four degrees in a direction a little east of north. 

 Smith's Fork cuts through the No. 1 almost parallel to its strike. The 

 beds here have the same general character that was noticed iu the sec- 

 tion given above. In some places on Saiith's Fork I noticed black coaly- 

 looking shales, and iu some of the laminated sandstones were ripple and 

 mud marks. 



Near the head of the south branch of Smith's Fork the gentle slope 

 of the Dakot^a group is broken and the stream flows through a small 

 canon caused by the breaking. Tnis caiion is marked a a on map B. 

 It is only about two miles long. On the west side the dip of the 

 strata is 5^, while on the east it is IS^^or 20°. In the latter place it 

 forms a small, almost triangular area, of which the base is toward the 

 west. The fracture determining this carton was probably the result of 

 a fold which may have been caused by igneous action, contemporane- 

 ous with the elevation of the trachytic hill opposite the mouith of the 



