28 GEOLOGICAL SUEVEY OF THE TERRITORIES. 



of four hundred feet, and above them are the Jurassic beds, with Pec- 

 ten, Belemnites densus, and a small species of Ostrea in great numbers. 

 The summit is capped with the thick layer of pudding-stone described as 

 occurring near the source of the Muddy, huge masses of which have fallen 

 on the side and at the base of the ridge, lookinglike gigantic boulders. One 

 of these masses is twenty-eight feet in all its dimensions, and is com- 

 posed of water-Avorn pebbles, varying in size from a grain of quartz to 

 an inch in diameter, set in a cement of sand. The large, amphitheater- 

 like area inclosed by the Eed Buttes and vicinity might be called an im- 

 perfect quaquaversal, composed of a number of anticlinals and partial 

 quaquaversals. On the north side of the Platte an anticlinal extends 

 off toward the northwest, showing in a small area the upper portion of 

 the Jurassic with a full development of the cretaceous. The two sides 

 come together in a distance of five or six miles and finally die out in 

 the plains. The Platte passes through this anticlinal. On the south 

 side of the river the two sides of the anticlinal are well shown, but 

 only the cretaceous and Jurassic beds are exposed. In the former are 

 four or five layers of sandstone with interpolated beds of. indurated sandy 

 clay, and separating the two formations is a massive bed of quartzite 

 or sandstone, of variable thickness as well as texture, ten to thirty feet. 

 On the east side of the Platte is quite a remarable gorge or canon, which 

 was first observed by the zealous photographer of the expedition, Mr. 

 Jackson of Omaha, and in whose honor we called it Jackson's Canon. 

 The waters of a former period (for the gorge is a dry one at the present 

 time) have cut directly down through the limestone, much as they 

 have at Box Elder and at the head of the Muddy. The gorge is two 

 hundred feet wide at the top, and sixty to seventy feet at the bottom, 

 and three hundred and fifty feet to four hundred feet deep. From the 

 canon the red beds incline in a series of ridges which form one-half 

 a circle. These red beds contain irregular seams of gypsum. Far 

 to the northwest the Big Horn Mountains can be dimly seen, and the 

 intermediate space between them and the Platte is slightly disturbed by 

 lines extending across the plain toward the range. These lines of dis- 

 turbance, or anticlinals, seldom bring to the surface rocks older than cre- 

 taceous. At Piney Butte the Jurassic beds are exposed over a very 

 small area. It appears that at this point the Laramie range breaks up 

 into several lines of disturbance, extending far across the plain toward 

 the Big Horn range. So far as I can ascertain, the ranges are there 

 more intimately connected than with any others to the westward. They 

 both form the outer or eastern border ranges. 



On the morning of the 26th we left our pleasant camp near the Bed 

 Buttes, and passed over the high ground to the westward, with the 

 Buttes on our left, and the ranges of the Big Horn dimly visible on our 

 right. In looking back from the west, eastward, on the ridge of which 

 the Bed Buttes form a part, we can see that the general dip is about 

 southeast or south, inclining gently down to the ifiain. About four miles 

 west of the Bed Buttes, on the north side of the road, are the most re- 

 markable semi-quaquaversals, one of which looks much like a crater. 

 The northwest side forms a perfect rim, while the southeast is open, 

 with a dry valley alongside, into which the materials within the rim 

 have been washed, so that it forms half an amphitheater, with the in- 

 closed space smoothed off and grassed over. The southeast end of Piney 

 Butte Bidge is separated by a synclinal, not more than one hundred 

 yards wide. The ridges form a complete half circle, and they extend 

 across the country far to the northwest. Between the Bed Buttes and 

 the Yellow Springs, a distance of sixteen miles, there is a series of low 



