MEDICINE BOW EANGE. 109 



Small grains of reddish-brown garnets occur in several localities; where 

 observed, they were always associated with the characteristic light-colored 

 gneisses. They were seen on French Creek 2 or 3 miles above the mouth, 

 near a small tributary coming in from the south ; also on the summit of 

 Deer Mountain. Gold in small quantities seems to occur in many districts 

 throughout the range. For several years, miners have been at work wash- 

 ing for gold on Douglas Creek. At Rock Creek Canon, fine yellow gold 

 has been obtained, and it is said to have been found also in Cooper Creek 

 Canon, and on the smaller streams that come down from the southeast side 

 of Elk Mountain. 



It will be readily seen that the larger rock-masses which form the 

 Medicine Bow Range present but comparatively few species among their 

 essential mineral constituents, however varied may be the lithological habit 

 of this great series of crystalline rocks. They embrace quartz, orthoclase, 

 plagioclase, hornblende, mica, chlorite, and carbonate of lime. As accessory 

 minerals, there occur garnet, epidote, magnetite, pyrites, cyanite, gold, and 

 calcite. Under the microscope, in addition to the above, were detected 

 zircon, apatite, and titanite. 



Conclusions. — The Archaean series of the Medicine Bow Range presents 

 many marked features characteristic of beds which have been referred to 

 the Huronian formation on the shores of Lake Huron in Canada, and in 

 various localities throughout the Appalachian chain. As these points of 

 resemblance are in many respects so strong, the greater part of the uplift 

 is referred to the same formation, with considerable hesitation, however, 

 as they are widely separated from any beds distinctly recognized as of 

 Huronian age, and such reference is based entirely upon lithological evi- 

 dences. It is also possible that they may simply be higher members of 

 the same great series with the Colorado Range. 



The Medicine Bow Range also presents many features which are 

 strikingly in contrast with the Laurentian rocks of the Colorado Range. 

 Although but few mineral species occur in the rock-masses of the one 

 range that are not found in the other, the relative proportions and dif- 

 ferences of arrangement of the constituent minerals is very marked. 



The Colorado Range, as already mentioned, is almost entirely formed 



