146 GEOLOGY AND MINING INDUSTRY OF LEADVILLE. 



several hundred feet of vertical beds which adjoin this on the ^yest it would 

 have been difficult, had no other opportunity for studying these faults 

 offered, to determine satisfactorily whether they belong to the series on 

 the eastern or those on the western side of the fault. Blue limestone 

 and White Porphvry are here — the former, it is true, represented only by 

 a comparatively thin bed; and the other metamorphosed rocks might as 

 \^■ell belong- litliologicallv to the bottom as to the top of tlie Weber Grits 

 formation 



The actual succession of vertical beds adjoining the cpiartzite crag on 

 the west is, as well as could be determined, the following : 



Feet. 



Ga|) siiowiiiji' .some black shale, about 40 



White Poii)hyry 20 



Blue limestone 8 



Quartzitic saudstones 100 



Bine limestone 8 



Quartzitic sandstones and decomposed greenish argilla- 

 ceous bcd.s, also silicious . 200 



In the description given of foults it is generally stated that the flexing, 

 occasioned by the movement of the foults, is reversed in the beds on either 

 side. For instance, if the strata on the side of the fault that is lifted 

 up are curved down by the dragging or friction of the movement, for the 

 same reason those on the other side, Avhicli moves relatively downwards, 

 would be curved upwards ; or if, on the other hand, on the upthrow side 

 of the fault the strata are curved upwards — as might be accounted for on 

 the supposition of a force pushing from behind against the fiiult plane — 

 then the beds on the downthrow side of the fault are curved downwards. 

 This is the generally accepted theoretical explanation of curving of beds 

 adjoining a fault. In this case, however, we have the alternative of assum- 

 ing that the beds curve downwards on both sides, or, what under the cir- 

 cumstances is even more improbable, that a bed of limestone, which everj-- 

 where else in the region examined has a thickness of 150 to 200 feet, has 

 in this single locality been reduced to eight feet. It was assumed therefore, 

 as shown on section D, that these vertical beds, as far as the c^uartzite crag, 

 belong to the series west of the fault and geologicall}- succeed the Weber 

 Grits in regular order ; that is, belong to the Upper Coal Measure horizon. 



