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



most difficult subject, upon which geologists are so much divided 

 in their views ; but it seems to me, that the theory so ably sup- 

 ported by M. Necker* and others, that mineral deposits are the 

 results of sublimation, is the most likely to be received. And it 

 is a theory, moreover, which meets with a most ready application 

 to ores of zinc, and particularly to the deposits of them at this 

 place. At Sterling, the red oxide of zinc forms a prominent 

 ridge, or wall, along the side of the hill, (as shown in the dia- 

 gram,) considerably above the adjoining bed of pure Franklinite, 

 appearing thus to have resisted the disintegrating process by which 

 immense quantities of the Franklinite have been crumbled into 

 a loose gravel, which so covers the ground as to destroy vegeta- 

 tion. This may be seen most conspicuously on a hill about fifty 

 rods west of the principal opening, where we are presented with 

 one vast, isolated mass, the origin of which I confess is not easy 

 to be explained. This fact must, however, be stated, and it may 

 have some bearing upon theory : — it is not accompanied by red 

 oxide of zinc, and it presents none of the characters of a bed or 

 vein, so far as I could discover. Is it a single isolated mass pro- 

 truded up from beneath, or has it gradually filled up, by sublima- 

 tion or aggregation, a once open space ? Its occurrence is similar 

 to the irregular beds of magnetic iron ore throughout this range, 

 and the occurrence of gneiss in close proximity with it, — an in- 

 variable accompaniment of the limestone wherever it bears the 

 ore, — seems to indicate a like origin for both the Franklinite and 

 the iron ore ; and it is remarkable, that when the limestone and 

 gneiss have thus become blended, we then find the rock well 

 sprinkled with various crystallized minerals, such as blue and 

 green spinelle, red and black garnets, &c., the fused appearance 

 of many of them fully attesting Iheir igneous origin. 



In conclusion, I have a few words to offer in regard to the eco- 

 nomical or commercial value of these zinc mines. It must be 

 understood that, although the Franklinite contains about 17 per 

 cent, of oxide of zinc, it is of no importance as an ore for reduc- 

 tion ; nor has it hitherto proved of any value as an ore of iron. 

 The red oxide is all that is proposed to be worked. This, as I 

 have intimated, does not occur in a pure state in masses of any 



* See his paper in the Proceedings of the London Geological Society, Vol. I, p. 

 392 J also Ansted's Treatise on Geology, Vol. II, pp. 271, et seq. 



