206 GEOLOGY AND MINING INDUSTRY OF LEADVILLB. 



at angles of from 15° to 20°, a conformable series, extending high up 

 into the Weber Grits, being still left uneroded on the summit of Little Ellen 

 Hill. 



In Section C, Atlas Sheet VIII, wliich follows nearly the northern 

 boundary of the map, the faults have apparently all been eliminated, and 

 the outlines of formations shown on the map owe their form entirel}^ to 

 folding and erosion. One broad anticline under the west slope of Pros- 

 pect Mountain and a shallow syncline in the Arkansas Valley express the 

 broader general features of folding. Near this line, at the moutli of the 

 east fork of the Arkansas, are found the westernmost actual exposures of 

 Paleozoic rocks within the area surveyed. These consist of beds belong- 

 ing to the Lower Quartzite formation, exposed in the bed of the stream and 

 in the cliffs south of it, dipping to the southeast. They constitute the most 

 definite evidence of the synclinal basin supposed to underlie the town of 

 Leadville. 



DISTRIBUTION OF PORPHYRY BODIES. 



Before proceeding to the detailed description of this region it will be 

 well to give a brief outline of the distribution -of the various porphyry 

 bodies, which form so important an element in its structure and have hlid so 

 great an influence upon its ore deposition. It is first to be observed tliat 

 the features of this distribution have a certain uniformity along nortliwest 

 and southeast lines in approximate parallelism with the line of major strike 

 of the sedimentary beds. As by far the greater portion of these bodies are 

 in the form of sheets either actually or approximately conformable with the 

 bedding of the inclosing sedimentary rocks, in cases where explorations 

 were insufficient to determine whether they were sheets or transverse dikes 

 the former has been assumed to be the case in drawing the ideal portion of the 

 various sections, and dikes have been indicated only when actual explora- 

 tions have proved that they were coming up directl}' from below. It may 

 readily happen, therefore, in the case of imperfectly explored bodies, that 

 future explorations may show the latter form to be more common than has 

 been indicated in the sections. 



White Porphyry. — The most important of these bodies is the AVhite Por- 

 phyry, which is generally found as a sheet immediately overlying the Blue 



