69 



To the northeast of this altered belt we trace another, occupy- 

 ing the northwestern side of the Mine Hill, east of the Wallkill 

 stream, a long narrow point of primary rocks, extending from 

 Pimple Hill to within about three miles of Hamburg. Not far 

 from the northeast termination of Pimple Hill, and near the old 

 Franklin furnace, we encounter, in the northwestern side of the 

 Mine Hill, next the valley of the Wallkill, a narrow belt of com- 

 mon gneiss rock, dipping, as usual, to the southeast. Reposing 

 upon this, with a conformable dip, is seen a highly interesting 

 mineral vein composed of impure magnetic iron ore, FranJdinite, 

 Garnet, Jejfersonite, and several other crystalline minerals, blend- 

 ed, especially near the borders of the mass, with the crystalline 

 limestone, much darkened and changed from its ordinary appear- 

 ance, by the amount of combined mineral matter ; much of this 

 calcareous portion of the vein is pervaded by small granular 

 crystals of the Franldinite. The whole vein has a thickness of 

 several feet. 



Immediately east of this metalliferous vein, there rests, in the 

 main body of the hill, a broad belt of the white crystalline lime- 

 stone, preserving its original, rather steep, southeastern dip. The 

 position of the vein here, is therefore, as in the majority of in- 

 stances in the region, intermediate between the primary strata 

 and the beds of altered limestone, which, notwithstanding the 

 partial fusion and intense heat to which it has been subjected, still 

 furnishes distinct traces of its lines of deposition. 



Towards the eastern declivity of the hill, the crystalline rock 

 prevails in considerable purity, though it is often very free from 

 foreign admixtures, even adjacent to the metalliferous vein. In 

 this latter position, however, it is more frequently mixed with 

 quartz, felspar, sahlite, augite, hornblende, and a great variety of 

 minerals, some of which are common ingredients in the primary 

 strata of the country. In the quartz, and near its contact with 

 the limestone, green spinelle occurs. 



The occurrence of so many of the minerals which are constitu- 

 ents of the adjoining 'primary rocks, both in the intrusive vein itself, 

 and in the neighbouring portions of the altered limestone, is a fact 

 of no little theoretical interest, as it leads us directly to views tend- 

 ing to explain satisfactorily the several sources of the numerous 



