STRUCTUKE OF NORTH IRON HILL. 401 



NORTH IRON" HILL. 



Atlas Sheet XXVI shows the topography, geology, and principal mine 

 developments of the northern end of Iron Hill, overlooking Stray Horse 

 gulch, and forms, as aforesaid, really a portion of the main map of Iron Hill. 

 In this region ore was first discovered on the Camp Bird claim in the 

 autumn of 1876. At present the principal mine workings belong to two 

 companies, the Argentine and the Adelaide, the former of which owns the 

 Camp Bird and Pine claims, and the latter the Terrible and Adelaide claims; 

 the latter overlaps those of the former company, a fact which has given 

 rise to much litigation. 



General geological structure. — As Compared with Irou Hill proper, its geo- 

 logical structure is one of extreme complexity, and also difficult of exact 

 determination, for the reason that underground workings are few and 

 accessible in but a comparatively small portion of the area. 



In the region west of the Iron fault the structure indicated on the map 

 is deduced from data obtained outside of its area, and to that extent is 

 theoretical. That the Blue Limestone basins up to the eastward as it ap- 

 proaches the fault is proved in the Devlin shaft, which reached it at a 

 depth of 200 feet, and in the Highland Mary and other shafts, in Stray 

 Horse gulch just north of the limits of the map, which found it still nearer 

 the surface. The outcrop indicated in the northwest corner of the map is 

 a portion of the Blue Limestone, split off from the main body, corresponding 

 to that cut in the Agassiz and adjoining shafts, and forming the south end 

 of the Little Stray Horse Park synclinal basin, as exjilained in Part I, 

 Chapter V. 



East of the Iron fault the formations rise slightly to the northward, so 

 that their strike assumes a more easterly and westerly direction and dips to 

 the south and east. By the erosion of Stray Horse gulch, on the lower 

 part of the steep northern slope of Iron Hill, a succession of Paleozoic for- 

 mations down to the Lower Quartzite are exposed, while by the movement 

 of the Adelaide fault, which crosses the northeast corner of the area mapped, 

 a still lower series of beds is exposed beyond it. 



MON XII 20 



