138 GEOLOGICAL SUKVEY OF THE TEERITOEIES 



are a beautiful pudding-stone of rounded quartz pebbles and feldspar, 

 and above it layers of fine siliceous rock, with thin intercalations of clay, 

 tlie whole having* the position and appearance of Potsdam sandstone. 

 I am inclined to believe that we have here Lower Silurian representatives. 

 In all cases these rocks repose on the upturned edges of the syenite, 

 sometimes nearly horizontal; again inclining 3° to 10°. In one or two 

 places these Lower Silurian beds are lifted a thousand feet or more into 

 the air, still maintaining a nearly horizontal position. On the mountain 

 sides the beds are broken off so as to incline 50°, 60°, up to nearly 90°. 



These -siliceous rocks, covered with ripple marks, &c, afford excellent 

 building stone, and are much used by the railroad company. They 

 reach a thickness of five hundred to eight hundred feet. Upon them 

 rests the blue limestone, thirty to forty feet thick; then variegated 

 sandstones ; and the red beds in the distance. 



From the tops of these ridges one can see numbers of both synclinal 

 and monoclinal valleys. There is one monoclinal valley, three to five 

 miles wide, which stretches far into the northwest, a smooth and level 

 grassy prairie. All these ridges have suffered great eroston, and the 

 Silurian beds are planed and grooved even to a greater extent than the 

 more recent beds. Everywhere the evidences of erosion during the 

 drift period are on a gigantic scale. 



A fine sulphur spring from under the bed of blue limestone gives 

 name to the station. The water is clear and possesses excellent medi- 

 cinal properties. 



Some very interesting specimens of native copper have been found in 

 this ridge, which at one time produced no small degree of excitement 

 among the inhabitants. The copper ore was found, on more careful 

 investigation, to be of no special economic value. It seems to occur as 

 a sort of chemical precipitate in the reddish triassic quartzite near the 

 summit of the ridge ; sometimes it is diffused through the rock in green 

 streaks in the form of green carbonate; sometimes coating large 

 masses of calcspar ; there are also very pretty dendritic impressions. 

 Near the copper mines are some heavy beds of red oxide of iron, which 

 must at some period become of great value to the country. The beds 

 are four to six feet thick, and though they appear to be local, yet a 

 great amount of ore could be taken out at comparatively small cost. 



It is an interesting fact that, although we are continually traveling 

 across what is usually regarded as the summit of the great Eocky 

 Mountain range, six thousand to seven thousand feet above tide- water, 

 yet this is the only locality along the road, between the Laramie Mount- 

 ains and the Wasatch Range, in Weber Valley, where we meet with 

 rocks older than Jurassic, and, except for a few miles near Lake Como, 

 none older than cretaceous. Rocks of ancient date seem to be the ex- 

 ception, while those of quite modern age, geologically speaking, prevail. 



Leaving Rawlings' Springs Station, the road passes through an anti- 

 clinal opening in the ridge, the south side inclining southeast 10° to 12°. 

 The lowest beds are yellowish-gray quartzose sandstones, overlaid by 

 carboniferous limestones. Still farther, south of the road, may be seen 

 the rounded hills composed of the cretaceous and tertiary beds, but the 

 intermediate formations, Jurassic and triassic, which are exposed on the 

 north side, are concealed. Perhai'-s the best example of an anticlinal 

 is seen soon after passing through the opening in the north side of the 

 road. The valley trends a little west of north, or northwest. It does 

 not show as distinctly on the north side of the road, with the exception 

 of the fragment of a ridge which is conspicuous on the south side of the 

 opening. Very soon the coal beds of the lower eocene appear on either 



