1 66 GEOLOGY AND MINING INDUSTRY OF LBADVILLE. 



quartzite and then cuts obliquely into the latter for a short. distance; it tlien 

 follows the bedding-plane for a few yards, and, again cutting across the 

 strata, disappears under the debris. The measurements were made with a 

 pocket level, checked by observations with an aneroid barometer, taken at 

 the base and again at the summit of the cliff; the discrepancy between the 

 two measurements amounting to only a few feet. 



Section from top of Sheep Mountain downward: 



Feet. 



White rorj)hyry, .300 to 400 feet. 

 C Blue Limestoue, brecciated at top, with abundant 



Lower Carboniferous . . \ secretions of black chert 180 



I Liahter-colored limestone "0 



L ^ 200 



^ Parting- Quartzite, fine grained, white 70 



Silurian \ ^^"l^ite Limestone, silicious at base, with white cherr 



1 secretions 160 



C 230 



^ lied cast beds 8 



I Shales, iuterbedded with "sandy limestones" 30 



I lieddish, finegrained sandstones, with indistinct im- 



Cambrian { pressions 40 



Gap.. ^^ 



I Quartzite 22 



j White Porphyry, 12 feet. 



/ White contact quartzite 05 



"^ 175 



C05 

 Archean G aeiss 



The total thickness here obtained of the lower Paleozoic series, which is 

 605 feet, is a little greater than that obtained at other points, which may possi- 

 bly be due to the swelling of the beds that would naturally succeed a com- 

 pression, if such exists, on the side of the fold next the fault. The contact 

 of the White Porphyr3^ and underlying Blue Limestone, which was here 

 visible over a considerable distance, was carefully studied, especially on the 

 side of the fold next the fault. The upper part of the Blue Limestone is 

 particularly dark and full of black chert. The actual line of contact is 

 marked by a l)reccia, whose character varies nmch. Now it is composed 

 mainly of White Porph)-ry fragments, then of chert, and again of a mixt- 

 ure of both with black shale or limestone. Sometimes arms of the White 



