ZINC ALONE. 175 



the surface, but it passed in depth into blende and was clearly an 

 oxidation product. In the others the blende came nearer the sur- 

 face. The ore follows the bedding planes and the joints normal to 

 these throughout a zone varying from 10 to 40 feet across and fills 

 the cracks. At their intersection the largest masses are found. 

 Six larger parallel fissures were especially marked at the Ueberroth. 

 This mine proved in development to be very wet, and a famous 

 pumping engine, the largest of its day, was built to keep it dry. 

 The Hartman and Saucon are less wet. A little pyrite occurs with 

 the blende, and thin, powdery coatings of greenockite sometimes 

 appear on its surface, but it is entirely free from lead and a very 

 high grade spelter is made from it. The mines were strong pro- 

 ducers from 1853 to 1876, but little has been done since. It is re- 

 ported (1891) that the great pumping engine has been started, and 

 they may once more furnish considerable quantities of ore. 



2.07.03. The mines were evidently filled by circulations from 

 below that brought the zinc ore to its present resting place in the 

 shattered and broken belt. Drinker considers it to have been de- 

 rived from a disseminated condition in the limestone. 1 



2.07.04. Example 28. Franklin Furnace and Sterling, N. J. 

 A bed consisting of franklinite, willemite, zincite, etc., in crystal- 

 line limestone, in many respects analogous to the magnetite of Ex- 

 ample 13. The franklinite and zincite beds are in a belt of white, 

 crystalline limestone which runs southwesterly from Orange County, 

 New York, across northwestern New Jersey. It was considered 

 metamorphosed Lower Silurian by H. D. Rogers, but its associa- 

 tion with Archaean gneiss is so close that it has with some reason 

 been regarded as of the same age with the gneiss. Beyond the 

 gneiss to the west a blue limestone supposed to be Lower Silurian 

 outcrops, and the same rock appears again to the southeast. F. L. 

 Nason, of the New Jersey Survey, has recently argued, after careful 



,and praiseworthy field work, and after discovering in unmetamor- 

 phosed portions some fossils which belong to the Olenellus fauna of 

 the Cambrian, that the blue and white limestones are of the same 

 age, and that the latter owes its character to a great dike of granite, 



1 F. L. Clerc, Mineral Resources, 1882, 361. Rec. H. S. Drinker. 

 "On the Mines and Works of the Lehi-h Zir.c Company," M. E., I. 67, 

 C. E. Hall, in Rep. D3, Second Geol. Survey Penn., p. 239. Die Gruben 

 und Werke der Lehigh Zink Gesellschaft in Peansylvanien, B. und IT* 

 Zeit., 1872, p. 51. 



