430 N. H. DARTON STRATIGRAPHY OF THE BLACK HILLS, ETC. 



overlap and fault cuts off the formation southwest of Colorado Springs, 

 but it appears again in the Canyon City region, where Cross found a 

 thickness of 300 feet, consisting mainly of pure white or gray sandstone, 

 usually friable, of uniform texture, and having a thin basal conglom- 

 erate. The hogback at this place is shown in figure 2, plate 34. Dark 

 shale layers are reported midway in the formation. Fossil leaves are 

 stated to occur in thin shale layers of various horizons, and Hatcher has 

 found saurian remains in the lower portion of the series in this region. 



The " Dakota " sandstone is prominent at the foot of Wet mountain, 

 southwest of Pueblo, where it has been described by Mr Gilbert.* its 

 greatest measured thickness, near Beulah, is 650 feet, consisting almost 

 entirely of sandstone, but the thickness in other portions of the area is 

 from 300 to 350 feet, and the sandstone contains beds of shale. The 

 basal portion usually is conglomeratic, sharply separated from the Mor- 

 rison clays or Fountain formation, which it overlaps locally, and at the 

 top there is a transition into the Benton formation. 



In the northern portion of Huerfano county and along the foot of the 

 Greenhorn mountain the formation is described by Hills as comprising 

 of 350 feet or more of sandstone, of which the lower two-thirds consists 

 generally of yellowish gray rock of coarse porous texture, with some 

 layers of fine conglomerate, commonly cross-bedded. This lower mem- 

 ber is separated from the upper by gray shales, from 100 to 150 feet in 

 thickness, and are light gray and fresh, fine grained, of close texture, 

 and regularly bedded. It lies in part on the Morrison formation, but 

 in places along the mountain front overlaps on the granites and schists. 

 The " Dakota" sandstone is a prominent feature in the foothills between 

 the Spanish peaks and Sangre de Cristo range, where for many miles 

 the sandstone is vertical and rises prominently as a " stone wall" above 

 the adjoining softer beds. 



BENTON GROUP 



The formations of the Benton group extend across eastern Colorado, 

 outcropping in a narrow zone lying next west of the Niobrara outcrop as 

 far south as the Arkansas valley, down which they extend for some dis- 

 tance, presenting outcrops of greater or less size mainly on the north 

 side of the valley. 



The thickness of the group is given as 600 feet at Platte canyon, 590 

 feet at Deer creek, west of Denver, 500 feet on Turkey creek, 580 feet at 

 Morrison, 400 feet one mile north of Morrison, 440 feet at Ralston creek, 

 348 feet at Bear canyon, 33 miles south of the town of Boulder, and 

 about 500 feet at Four-mile canyon. It is about 640 feet east of Lyons. 



* Pueblo folio, cit. 



