132 GEOLOGICAL SURVEY OF THE TERRITORIES. 



creek. Between the canon and station No. 38 there are two areas of 

 trachytic rock,which may also have had something to do with it. On the 

 south side of the Grand Canon the Dakota group does not appear at 

 the upper end, shales of higher positions abutting against the schists, 

 as shown in Fig. 2, Plate VII. 



In the angle included in the great bend of the Gunnison, opposite the 

 mouth of Smith's Fork, the sandstones of No. 1 form the surface. Sec- 

 tious across this area are shown on Plate VIII, the letters giving the 

 liues on which thej T are made, as represented on map B. On the west 

 side of this area the beds dip steeply, and in the valley of the Uncom- 

 pahgre the Dakota group is covered with the overlying beds of later 

 origin. 



A short distance above the mouth' of Boubideau's Creek it appears 

 again, forming bluffs that gradually rise as we go down until the river 

 is again in canon (Unaweep Canon.) 



The following is a section of the bluff on the Gunnison opposite the 

 mouth of Boubideau's Creek : 



No. 12. — Section of Cretaceous No. 1. — Bluff on Gunnison River. 



Thickness 

 Top. m. In. 



1. Space reaching from the top of the bluff, which is covered with bowlders 



of sandstone and volcanic rock, underlaid, in all probability, with sand- 

 stones and shales 50to60 



2. Massive yellow sandstones '. 10 



3. Space in which the upper part is occupied with gray and rust-colored 



sandstone sbales, with carbonaceous material. The lower portion of the 

 space is probably filled with layers similar to those above. The slope is 

 covered with the debris of sandstones in which there are fragmental im- 

 pressions of stems, but no leaves, although careful search was made.. 31 



4. Gray laminated sandstones 33 



5. Black carbonaceous or liguitic shales with effioresence of alkali 16 



6. Yellow and gray shaly sandstones 4 



7. Fine black carbonaceous shales 6 



8. Massive gray sandstone 10 



9. Shaly sandstones alternating w r ith shales like those of No. 5 22 



10. Coarse, white, granular siliceous sandstoue 2to 4 



11. Sandstone shales reaching to the base of the bluff 1 16 to 18 



Base. 



Total, about "-. 199 6 



This represents only a portion of the No. 1. The river, however, soon 

 cuts through to its base. The area occupied along the eastern side of 

 the Gunnison by the Dakota group is limited to a narrow belt, the 

 higher beds outcropping in low bluffs from three to five miles from the 

 river. 



A section at station 60 is given below : 



No. 13. — Section of Wo. 1 Cretaceous. — Bluff on east side of Gunnison 



River, Station 60. 



Thickness. 

 Top. Ft. In. 



1. Massive yellow siliceous sandstones, with indistinct impressions of leaves 



and stems. The sandstones are so coarse that nothing recognizable 



could be seen 54 



2. Blue argillaceous shales, gypsif erous 6 



3. Fine black liguitic shales with interlam mated sandstones and clays 18 6 



4. Blackish-gray laminated sandstones and shales 31 8 



5. Soft gray sandstones with greenish shales in the upper part 25 4 



6. Soft argillaceous sandstone shales in bands of red and green colors alter- 



nating 25 4 



7. Yellow siliceous sandstones in rather massive layers, very much like those 



in No. 1, given above 63 



8. Blue and yellow mottled argillaceous sandstone shales 6 4 



9. Fine red and green shales, argillaceous and probably calcareous 5 10 



