194 GEOLOGY AND MINING INDUSTRY OF LEADVILLB. 



continuous one as would result from the erosion of running water, but is 

 comparatively gentle for a considerable distance from the head and then 

 descends abruptly into the valley of the Arkansas. 



Along the western slopes of Buckeye Peak, as already mentioned, are 

 two principal bodies of quartz-porphyry, apparently interstratified in the 

 Weber Grits, which extend northward beyond the limits of the map. East 

 of these are several irregular bodies of the same rock, whose outlines are 

 given on the map with tolerable accuracy. They are probably connected 

 in origin with the large laccolitic mass of Eagle River Porphyry which lies 

 just beyond the border of the map to the north. They are in part inter- 

 stratified, but little satisfactory evidence was obtained bearing upon their 

 underground extension. In the basin between Chalk Mountain and Chicago 

 Ridge, whose waters drain into Eagle River, a synclinal fold can be dis- 

 tinctly traced, which basins up to the southward. Its outlines are well 

 marked by an interbedded sheet of Eagle River Porphyry. The inclination 

 of the fold is comparatively shallow on the west, though in some places dips 

 of as high as 25 are observed; while on the east the angle is still steeper, 

 as shown in Section A, Atlas Sheet VIII. In its trough above the por- 

 phyry is a small bed of limestone. 



chalk Mountain. From the head of the straight north and south portion of 

 Arkansas Valley projects a singular ridge, like a huge railway embankment, 

 prominent by its brilliant white color in the somber surrounding of pine 

 trees From the material of which it is composed and which, in the fact 

 that it is soft and white, has a certain resemblance to chalk, the person who 

 first settled at its base gave to his home the name of Chalk Ranch. At 

 this point the Arkansas Valley bends sharply to the eastward and its level 

 rises abruptly 100 feet or more; while the direct northern continuation of 

 the valley below is formed by a still more elevated valley, the bed of a 

 little stream known as Chalk Creek, which a short distance above Chalk 

 Ranch falls in a picturesque cascade from the upper valley level into a 

 deep narrow basin and flows in a narrow gorge to join the Arkansas just 

 bjlow the ranch. The Denver and Rio Grande narrow-gauge railway, in 

 order to gain grade enough to overcome this sudden elevation of the valley 

 level, climbs gradually along the western wall of the Arkansas Valley, 



