470 
GEOLOGY OF THE FIRST DISTRICT. 
white, and highly crystalline, and contains disseminated scales of graphite. This line of 
altered rock ranges southwestward nearly to the turnpike, and is met with again on the road 
to Sparta', about half a mile beyond the turnpike. 
“ Between the small knob of gneiss, above spoken of, and the Walkill mountain, to the 
southeast, we meet with another deposit of brown or hematitic iron ore, a little beyond the 
termination of the crystalline limestone, none of which, however, is discovered near it.” 
“To the northeast of this altered belt we trace another, occupying the northwestern side of 
the Mine hill, east of the Walkill stream, a long narrow point of primary rocks, extending 
from Pimple hill to within about three miles of Hamburgh. Not far from the northeast ter¬ 
mination of Pimple hill, and near the old Franklin furnace, we encounter, in the northwestern 
side of the Mine hill, next the valley of the Walkill, a narrow belt of common 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, franklinite, garnet, 
jeffersonite, and several other crystalline minerals, blended, especially near the borders of the 
mass, with the crystalline limestone, much darkened and changed from its ordinary appearance 
by the amount of combined mineral matter. Much of this calcareous portion of the vein is 
pervaded by small granular crystals of the franklinite. 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 limestone, preserving its original, rather steep, southeastern 
dip. The position of the vein here is therefore, as in the majority of instances in the region, 
intermediate between the primary strata and the beds of altered limestone, which, notwith¬ 
standing 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 constituents of the d.6iommg primary 
rocks, both in the intrusive vein itself, and in the neighboring portions of the altered limestone, 
is a fact of no little theoretical interest, as it leads us directly to views tending to explain 
satisfactorily the several sources of the numerous and varied crystalline minerals found con¬ 
nected with the changes effected in the limestone. 
“ At the summit of the ridge there is a seam of quartz rock, presenting some indications 
of its occurring as a vein in the white limestone. Its nature and origin cannot be proved, for 
it may be a vein of mineral matter strictly intrusive, or one of the beds of chert, so common 
in the limestone, or a portion of Formation L, completely fused by contact with the intensely 
heated metalliferous vein. The confused arrangement and varied aggregation of the altering 
and altered materials at this place, render it next to impossible to trace the true relationship 
