41 G GEOLOGICAL EXCURSION TO THE ROCKY MOUNTAINS. 



turn to the southeast in Elbow canyon, crossing the upturned Red Beds 

 and entering a narrow syncline in Cretaceous rocks. In this syncline 

 the Dakota sandstones are strongly developed and contain some coal 

 scams. They are overlaid by the black shales of fche Middle Oretace- 

 ous; the uppermost hard bed seen in the axis of the syncline is prob- 

 ably the Niobrara limestone, which is always a well marked horizon. 63 



The southeast course is maintained until the Bed Beds appear again 

 from under the syncline. when the road takes a more easterly course 



for about 10 miles (16 km.) across an area of rounded hills formed of 

 Upper and Middle Carboniferous beds, already showing a larger pro- 

 portion of grits in the vicinity of the ancient shore line of the Sawatch 

 upheaval. 



The road then enters Eagle River canyon, which it follows in ;i south- 

 east course for over l.") miles [24 km.). This picturesque gorge is cut 

 along the north and northeast Hanks of the Archean uplift of the 

 Sawatch. Its bottom, which is from 1.(100 to 1,500 feet (306 to 457m.) 

 below the level of the surrounding country, is generally in the under- 

 lying granite and gneiss, the summits of the cliffs being formed of 

 Cambrian quartziteSj and Silurian and Lower Carboniferous limestones, 

 winch dip 10° to 15° to the northeast, succeeded in the higher hills (,, 

 the north by several thousand feet of grits and sandstones of .Middle 

 and Upper Carboniferous age. The aggregate thickness of the Lower 

 Paleozoic series, up to and including the Lower Carboniferous, is only 

 about 600 feet (183 m.), of winch about 300 feet (ill m.) are quartzites. 



Shortly after entering the canyon, shaft houses of various mines are 

 seen perched high Up on the cliffs to the north of the road, from which 

 long aerial wire tramways for the transportation of ore reach down to 

 the level of the railroad. These are a portion of the mines of Battle 

 mountain in the Led (Miff mining district, whose ores are shipped 

 from Rock Creak and Red Cliff' stations to various smelting works 

 throughout the country. 



Bed Cliff Mining District.— The ores of this district are found at two 

 distinct horizons, without any visible connection between them. 



The first are bodies of iron pyrite with argentiferous galena, in the 

 bower Carboniferous or Blue dolomitic limestone, beneath an intrusive 

 sheet of quartz-porphyry. They occur in immense bodies as a replace- 

 ment of the limestone, but are generally of rather low grade. The 

 manner of successive alteration of such ores by surface or oxidizing 

 waters through sulphates to oxides can be remarkably well seen iu 

 some of the mines/' 5 



The second horizon is l>0() to 1300 feet (01 to 91 m.) lower geologically, 

 at the top of the white Cambrian quartzite, The ores are in smaller 

 volume and more irregular in distribution, but very much richer. They 



