70 GEOLOGICAL SUEVEY OF THE TEERITOEIES. 



CHAPTER ly. 



FEOM ELK MOUNTAINS TO MIDDLE PARK. 



After a prelimiuary exploration of the Elk range was completed, the 

 party returned by way of Twin Lakes around the Arkansas Valley and 

 across the divide by way of the Tennessee Pass. 



As we pass up the valley and examine the comparatively smooth ter- 

 races that are well shown on both sides, as well as the wooded foot-hills, 

 we form no conception of the deep gorges or caiions which are found 

 between the mountain-crests. Above the entrance of Lake Creek into 

 the Arkansas, the valley is quite wide, though the immediate bottom is 

 narrow, but the evidence of erosion in the subsequent deposits of de- 

 trital matter is very marked. Just opposite Massive Mountain the 

 river-bottom is about a mile in width ; then a terrace rises 40 feet above, 

 and a second terrace of 500 feet, composed of horizontal strata of sand, 

 clays, sandstones, and conglomerates, a kind of modern lake-deposit. 

 The distance between the immediate base of the Park r ange on the 

 east side of the Arkansas and the Sawatch on the west side is about 

 ten miles in a straight line. A coarse bowlder-drift or detritus covers 

 the foot-hills to a considerable depth, while beneath are the worn surfaces 

 of the granite rocks, which have most probably been ground down from 

 their lofty heights by the old glaciers that once filled the valley. 



The evidence shows that the waters of the Post-pliocene lake were 

 1,200 to 1,500 feet above the present river-bed. In the mountains to 

 the west of the pass some valuable silver-mines have been discovered, 

 and the Homestake district laid out. Very little is known of them as yet, 

 except that about seventy tons of ore have been taken out and trans- 

 ported to a smelting-furnace near Denver. The yield is rejDorted to be 

 from $100 to $200 of silver per ton of ore. The Tennessee Pass forms 

 the water-divide between the sources of the Arkansas and some of the 

 south branches of the Blue Eiver, as the Roaring Pork. The height of 

 the pass is 10,223 feet above sea-level. 



The country on both sides of the divide is covered quite thickly with 

 pines, with here and there openings like meadows. The pine-forests are 

 destroyed more or less every year by fires, which sweep over large areas. 

 Unless the autumnal fires can be checked, the pine-forests of all these 

 mountain-districts must disappear. 



At the present time the various branches of the Arkansas are choked 

 up with ties which are to be floated down the main river toward Pueblo 

 for the use of the Atchison, Topeka and Santa F6 Railroad. 



Remnants of the sedimentary rocks appear here and there about the 

 divide, but the basis rocks are so covered with debris or detritus that it 

 is hardly possible to determine them. It is most probable the granitic 

 rocks prevail. As we descend the west side of the pass in the narrow 

 gulch of Eagle Creek the gneisses, with well-defined bedding, are seen on 

 both sides for two miles, when patches of stratified quartzites occur, 

 resting on the upturned edges of the gneisses. 



About ten miles below the Tennessee Pass, on Eagle River, on the 

 sides of the gulch, we have gneiss, with dikes of trachyte; white quartzite 

 stratified, 30 feet ; reddish quartzite, full of seams of white quartz and 

 much changed by dikes. The quartzite passes up into a quartzose 

 sandstone, rather coarse, 100 feet ; yellow-brown arenaceous mud, lime 

 stone alternating with seams of shale and quartzite ; coarse and fine 

 sandstone of various textures, with layers of limestone interstratified^ 



