PEALE.] GEOLOGY SECTIONS OF DAKOTA GROUP. 133 



Bass. Thickness. 



Ft. In. 



10. Compact, fine-grained, brownish-red sandstones, witli interlaniinated 



shaly beds with a cross-fracture 47 6 



11. White,' dendritic, argiliaceous sandstones, indurated near the top, and 



having a sharp, conchoidal fracture 8 



12. Greenish and purplish argiUaceous shales 19 



13. Yellow siliceous sandstone, I'ather massive in the lower part, laminated 



above 6 4 



14. Eeddish and whitish-green mottled sandstones, grading up into soft 



shales 8 



15. Eeddish, purplish, and greenish sandy shales, mottled 24 



16. Greenish-white, argillaceous sandstone, weathering into rounded^ 



masses like bowlders ! 



17. Brick-red shales mottled with green ! ^g c^ 



IS. Pink sandstone, 1 foot [ 



19. Greenish shaly sandstones, with hard bauds of sandstone at intervals, | 



and fine red shales in laminie, 6 inches in thickness J 



20. Soft greenish conglomeritic sandstone. The upper bed is a green sand- 



stone, below which is au irregular mottled limestone, argillaceous, 

 brown, reddish, and greenish, with jasper in center of nodules lu the 

 center there are also quartz and calcite. Some of the beds in this space 

 are concealed 43 



21. Massive yellow siliceous sandstone, coarse in places, with siliceous peb- 



bles :... 10 



22. Soft white sandstones, conglomeritic at the base, containing black, red, 



and yellow pebbles ; very fine, 1 6 



23. Soft shaly beds, partially concealed by argillaceous Mhris. These beds 



are composed of greenish-gray, argillaceous sandstones, brownish nod- 

 ular limestone, and greenish clays. Nearly all the beds are gypsifer- 

 ous. The sandstones break into rounded pieces. The debris is coated 

 with a salty, alkaline efiiorescence 30 



24. Space in which the slope is partially 'covered with d^firis of hard red 



sandstone and dark gray sandstone, and indurated argillaceous beds 

 of a purplish sandstone ; near the top was an outcrop of dark brown- 

 ish-gray sandstone. In the debris below I found a specimen Sassafras, 

 like S. mirahile, in a rock similar, but was unable to find any fossils in 

 place 55 



25. Yellowish siliceous sandstones, generally in massive beds, but toward the . 



base somewhat laminated , 100 



Total about 651 



I tbink it likely that most of tlie argillaceous beds given above in 

 the section are calcareous. I had no means of testing them on the spot. 

 The nodalar bed of limestone in No. 20 is identical with that in No. 7 

 of the section No. 11 at station 73. The jaspery pebbles are the same. 

 They are bright-red and have calcite in cavities in the center of irreg- 

 ular masses. The calcite is deep yellow. 



There is a partial outcrop of the Dakota group in the bluff between 

 the Gunnison and the Grand at the mouth of the latter. The following 

 is the detailed section at this point : 



No. 14. — Sectio/i of No. 1 Cretaceous. — Bluff on Gunnison near the mouth. 



Thickness. 

 Feet. 



1. White siliceous sandstone at base of bluff. Thickness could not be ascer- 



tained, only upper part showing 



2. Fine black lignitic shales 5 



3. Gray siliceous sandstone with shaly beds ^ 



4. Beds of soft friable lignite with bands of dark greenish-gray sandstone I 



filled with fragments of stems and carbonaceous material. These | 

 sandstones are in bands of one foot to two feet thickness. The lig- } 150 to 160 

 nite is of x^oor quality, decomposing rapidly on exposure to the at- 

 mosphere 



5. Yellow silici^ous sandstones with massive structure below and becom- 



ing shaly above. The lower portion is gypsiferous J 



Total 155 to 165 



