256 On the Zinc Mines of Franklin, N. J. 



fore affirm that the only deposit of oxide of zinc at present known 

 to mineralogists, is in Sussex County, and is there circumscribed 

 by the limits above stated. At Sterling, the ore beds appear on 

 the east flank of the limestone hills, while at Franklin, four miles 

 to the north, they are on the west side, — the great belt of the 

 limestone, as it extends through the valley in this direction, being 

 thrown considerably to the east of the line of its direct prolonga- 

 tion at Sterling, while the same relations, as to the order of oc- 

 currence, are observed between the beds of zinc and the rock at 

 both places, as well as at all the intermediate points where they 

 have been penetrated. The strata ©f limestone run nearly north- 

 west and southeast, dipping at an inclination from the vertical, 

 70° to 80° to the eastward. The direction and dip correspond 

 here with the strata of gneiss, though deviating in other places, 

 by causes of paroxysmal action, which have intruded masses of 

 gneiss through the limestone, and destroyed its continuity of stra- 

 tification ; sometimes forming a blended mass of both materials, 

 and including large and shapeless deposits of magnetic iron ore. 

 This rock is the altered limesto7ie* of Prof. Rogers, who has most 

 ably treated of the various phenomena relating to it, in his report 

 on the Geology of New Jersey, to which the reader is referred. 



I remark, that the relations between the beds of ore and the 

 rock are always the same ; and here I would not have it under- 

 stood that there are several disconnected and parallel beds of zinc 

 ore, regularly interstratified with the limestone beds, but that 

 there is, in fact, only one bed — this being made up of t/wee con- 

 tinuous parallel divisions. When we have penetrated the outcrop 

 of limestone at Sterling, on the east side of the hill, we first come 

 to an outer belt of from three to seven feet in thickness, consisting 

 of nearly equal parts in bulk, of red oxide of zinc and Franklinite.f 

 Second, in close contact with the mixed ore, but no where 

 blended with it, we meet with a thin seam of brownish-black fer- 



* A member of the lower secondary, or Apalachian rocks, of Prof Rogers. It 

 presents great diversity of aspect and composition, but has never been found to con- 

 tain fossils when in close proximity with the iritruded igneous dykes and beds. In 

 fact, the fossiliferous character of this limestone is shown only in one or two very 

 remote patches, pointed out by Prof Rogers, which thus derive great interest by 

 characterizing the whole formation. 



t The actual proportion, by weight, as determined by pulverizing a quantity, 

 and carefully separating one from the other by a magnet, I found to be a little 

 over 60 percent, of red oxide. 



