82 GEOLOGICAL SURVEY OF THE TERRITORIES. 



this ridge, which is 1,500 to 2,000 feet above the river. Its rim is made 

 of the sandstone of No. 1 Cretaceous (Dakota group), which crosses 

 the river at the head of the canon, almost at right angles to its course, 

 the dip being in the direction of the stream. On the north side there 

 is a curious spoon-like curve in the strata, shown in Plate II, which will 

 be fully explained in Mr. Marviue's report, as it is in his district. Be- 

 neath the Cretaceous sandstone, in place, are the Jurassic shales aud 

 limestones, followed by the Eed Beds, (Triassic?) underneath which is 

 a series of gypsiferous beds, exposed on both sides of the river. These 

 will all be referred to again when I come to speak of the various for- 

 mations separately. 



The river, on leaving the canon, keeps the course it has there until 

 it reaches the Grand. The valley is about twelve miles long, extending 

 to within five or six miles of the Grand. It is wide and bordered with 

 low hills of gypsiferous shales, covered with a growth of cedar ( Juniperus 

 occidentalis). Beyond these hills are higher ones, not reaching above 

 timber-line, the basis being red sandstones. The gypsum hills are con- 

 spicuous from their white color and their softness, which causes them to 

 yield readily to eroding influences. They are therefore much cut 

 up by gullies which for the greater portion of the year are dry, but during 

 storms are the beds of torrents washing down the soft clay. Each creek 

 extending into them, fans out into a great number of small gullies. The 

 shales and sandstones of which they are formed belong to the same hori- 

 zon, viz, Carboniferous or Permo-Carboniferous, as do those mentioned 

 as occurring below the Red Beds above the canon. 



It seems as though the Eagle, instead of entering the canon and cutting 

 its way across the hard sandstone of the Dakota group, should have 

 worn its channel through these softer beds that lie to the southward of 

 its present course. It might perhaps have done this, but that an island 

 of eruptive rock (basalt), of great hardness, caps the hills south of the 

 carton (see map A), forming a barrier that in all probability determined 

 its deflection to the northward. Fig. 1, Plate II, represents a section 

 across this area from the Eagle to creek g. 



There are two large creeks flowing into the Eagle from the south in 

 this lower valley. The first or eastern one I will designate as creek g, 

 and the other as creek h. They both have their origin in abroad-topped 

 ridge of red sandstone (Triassic ?) which forms the divide or water-shed 

 between Frying-Pan Creek, a tributary of Roaring Fork, and the waters 

 of the Eagle. In 1873 we made a station (No. 82), on this ridge, and 

 from it I made a section,* showing the structure of the country as it ap- 

 peared to be looking northward. I said, in the report,t that there 

 seemed to be a series of faults aud that the section might have to be 

 modified when the region should have been more closely studied. 



I found this year that the beds I then thought to be Cretaceous, judg- 

 ing from the color as seen from the station on looking north, are really 

 the gypsiferous beds that lie beneath the red sandstones. Instead of a 

 number of faults, therefore, as shown in the illustration (Fig. 3, plate 

 19, Report for 1873), there is simply an exposure of the gypsum-beds in 

 both the places marked " Cretaceous," at the head of creek h and in the 

 valley of Eagle River. As I mentioned in my notes of last year, the 

 red sandstones on station 82 dip a few degrees west of north, inclining 

 at a comparatively small angle, which increases as we go northward. 

 On station 8, the dip is in the same direction, as also on station 9. As 



* Plate 19, Fig. 3, 7th Annual Report, 1873. 

 t Page 266, 7th Annual Report, 1873. 



