1869.] ^"^ [Hayclen. 



east of Eawlings Springs I obtained tlie same Inoceramus and a large 

 species of Ammonite, These fossils are important in establishing the 

 age of these rocks. 



At Rawlings' Springs are some very interesting geological features. 

 At this locality the elevatory forces Avere exerted more powerfully than 

 at any other i^oint along the railroad from Laramie Station to Green 

 river. The entire series of rocks are exj)osed here, from the syenites to 

 the cretaceous inclusive. The railroad passes through an anticlinal 

 opening. To the south of the road are variegated gray, brovrn and red- 

 dish siliceous rocks dipping 5^ to 10° S. W. A very hard bluish lime- 

 stone resting upon them I have no doubt is carboniferous, although I 

 Avas unable to find any fossils in this region. North of the road ridges 

 of upheaval stretch away toward the nortli-west and attain a height of 

 1200 to 1500 feet above the road. On careful examination the red syenite 

 may be found exposed in a number of places, and gives us the opportu- 

 nity of studying the relation which the unchanged rocks sustain to the 

 metamorphic. The syenite beds dip 70° about S. E., the unchanged beds 

 resting upon them in nearly a horizontal isosition. The layers imme- 

 diately on the syenite are a beautiful pudding stone of rounded quartz 

 pebbles and feldspar, and above it layers of fine siliceous rock with thin 

 intercalations of clay, the whole having the position and appearance of 

 Potsdam sandstone. I am inclined to believe that we have here lower 

 Silurian rejpresentatives. 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 thou- 

 sand feet or more into the air, still maintaining a nearly horizontal pos- 

 ture. 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 500 to 800 feet. Upon them rests the blue lime- 

 stone, 30 to 40 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, 3 to 5 miles 

 wide, which stretches far into the north-west, a smooth and level grassy 

 prairie. All these ridges have suffered great erosion, 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 medicinal 

 properties. 



About 4 miles west of Eawlings' Springs the tertiary beds begin to 

 overlap, but in the distance on either side are lofty ridges of cretaceous 

 and perhaps still older rocks. The ridge, 15 miles south of Separation, 

 at least 1000 feet high, is certainly formed of lower cretaceous and prob- 



