396 GEOLOGY AND MINING INDUSTRY OF LEADVILLE. 



and in places reaching a depth of 40 feet or more below the actual contact 

 of limestone and porphyry. 



In Section C, which passes through the North incline of the Bull's 

 Eye, and a little south of the South incline of the Iron mine, the tendency 

 of the rich ore to accumulate above a fold in the limestone, which has 

 already been noticed in the Rock and South Bull's Eye, is quite apparent, 

 the barren zone occurring on the steeper dip of the formation towards the 

 Silver Cord claim. 



In the section through the Main incline the folds are less prominent, 

 but the same tendency always holds good, and it is one of the practical 

 generalizations made by those working in the mine that rich ore bodies 

 occur always in troughs of the limestone. The steeper dip of the forma- 

 tion beyond the accumulation of rich ore is quite evident. Just below the 

 seventh level a small body of Gray Porphyry crosses the Main incline diag- 

 onally in a direction a little north of east. Here the incline is some dis- 

 tance below the contact, and it could not be definitely determined whether 

 the porphyry extended up to the contact or not, though it has unintention- 

 ally been indicated as doing so in the section. To the westward, if it con- 

 tinues in that direction, it does not, as the contact has been explored on the 

 line of its continuation without finding it. It is cut in the eighth level a 

 short distance north of the Main incline, but in neither case is the limestone 

 mineralized to any extent at its contact. 



On the line of the North incline the general dip of the formation has 

 become extremely shallow, as shown by the old drift, known as the Tucson 

 incline, which followed the contact in all its curves and irregularities. This 

 shallowing of the dip is probably due to a general basining-up of the for- 

 mation to the northward, since on North Iron hill in the Adelaide and Argen- 

 tine ground it curves in strike to the eastward and assumes a southerly 

 dip. Thus at the Hynes shaft, which is on the same line of strike with the 

 Tvicson shaft, the contact stands about fifty feet higher than at the latter. 



In this portion of the mine a second series of less important ore bodies 

 occurs in a depression in the limestone to the west of the main bonanza 

 and near the fault line. It has, like the latter, a general northeast trend. 



