RELATION OF DEFORMATION TO DEPOSITION OF ORE. 27 



elusion that " the ore-deposits usually, possibly not universally, occupy depressions 

 in the strata."* 



Kelation of Deformation to Deposition of Ore. 



Position of Accumulations of Ore. — According to the generally accepted view of the 

 accumulation of the ores by lateral secretion or leaching, it is not strange that the 

 heavier deposits are found in the depressions where we should expect them to be, 

 but it is not clear to me in the cases cited that the flexing of the beds, the synclines 

 and anticlines, are due only to the original inequalities in the ocean floor and are 

 not accompanied by any fracturing or displacements. Do we not have in the 

 broken, brecciated beds evidence of disruption ; and is it clear that in all cases 

 these depressions are not monoclines ending in faults? We may also ask whether 

 we do not find the simplest explanation of the inequalities of the strata to be that 

 they have been subjected to uplifts and downthrows occurring in all the ages from 

 early Silurian time onward ? A line of break and movement once established at 

 an early j)eriod would no doubt be perpetuated in succeeding formations, and would 

 explain many of the observed phenomena of thinning out locally of some of the 

 strata and their want of horizontal continuity. 



Examples of Faulting. — A few examples which have fallen under my observation 

 may here be cited. 



In addition to two or more abrupt transitions visible horizontally in the levels 

 of the Helena mine f from the horizon of the quarr3'^-rock and oil-rock of the 

 upper Trenton limestone to the lead and zinc-bearing beds of the Galena dolo- 

 mites, we have a fine example of a dislocation, open to the surface, about a 

 quarter of a mile west of the Helena mine, in the left bank of the Shullsburg 

 creek, just east of the line of New Diggings township. At that point there is a fine 

 exposure of the Trenton limestone — the '' quarry-rock " — in a bluff" rising abruptly 

 from the water to a height of from 10 to 20 feet. The strata, which appear to dip 

 westward, rise gently eastward as far as a little dell or ravine descending from the 

 southward, where the limestones disappear from view. On the other side of this 

 ravine about 100 feet away a tunnel driven in at the creek level passes into the 

 coarsegrained Galena dolomites and gives access to a long stretch of zinc and lead- 

 bearing ground trending southeasterly, following crevices known to the miners as 

 *' 10 o' clocks," being nearly at right angles with the general northeasterly trend of 

 the main ore-bearing crevices of the Helena mine and parallel with two other 

 known northwesterly crevices. 



Beyond this tunnel to the east the Trenton limestone is again found. It would 

 thus appear that a block of Galena dolomite has here dropped below the horizon 

 of the Trenton on each side of it. The displacement is not very great, but it ap- 

 pears to be a veritable fault, or a compound fault, accompanied by heavy mineral- 

 ization of the Galena dolomites. It occurs so abruptly and within such a limited 

 distance as to preclude the idea of a flexure of the beds. 



Examples of evident dislocation might be multiplied, but one instance such as 

 here cited will, I think, suffice to establish the fact that disturbances of relative 

 level do exist,]: and in direct connection with mineral deposits. 



*0p. cit., p. 438. 



fOne of the properties of the Wisconsin Lead and Zinc Company and situated three miles west 

 of Shullsburg on Shullsburg creek. 



JThe recent paper, Some djmamic Phenomena shown by the Baraboo quartzite Ranges of cen- 

 tral Wisconsin, by C. R. Van Hise : The Journal of Geology, vol. i, no. i, 1893. p. 347, has a bearing 

 upon the questions at issue. 



