472 
GEOLOGY OF THE FIRST DISTRICT. 
separation of the zinc from the franklinite in this ore, still remains, however, a desideratum 
in practical metallurgy. 
“Between Sterling and Sparta, the belt of crystalline limestone is traceable with but little 
interruption nearly the whole distance, affording in some places specimens of a variegated 
marble of uncommon beauty. It follows the eastern base of Pimple hill to the southwestern 
termination of that ridge, and then appears nearly in the same line at several points on the 
west of the gneiss hills, west of Sparta, and also within a few hundred yards of the town itself. 
The narrow valley embraced between those hills and the Walkill mountain on the southeast, 
is, in the immediate neighborhood of Sparta, and for some distance southwest, occupied by 
the unaltered blue limestone dipping usually towards the northwest. 
“ About a third of a mile northwest of Sparta, the white crystalline limestone crosses the 
turnpike road. This is one of the principal localities whence mineralogists have supplied 
their cabinets with specimens of chondrodite or brucite. A better locality, howeverTmay be 
seen on the west side of the hill, about half a mile further north, where another exposure of 
the white crystalline limestone affords crystals of the brucite and grey spinelle in an abun¬ 
dance, and of a quality far surpassing those of any other spot yet discovered in this vicinity. 
At the same place might be opened inexhaustible quarries of variegated and pure white mar¬ 
ble ; some of the former promising to be, if polished, of uncommon beauty. Care should 
be observed, in establishing quarries in this rock, to choose those parts of the belt least shat¬ 
tered by the action to which it has been exposed. 
“ Between three and four miles southwest from Sparta, on the northwest side of a low 
ridge of gneiss, we find a very interesting locality of the altered limestone, very nearly in 
the prolongation of the belt which passes along the southeast base of Pimple hill. This spot 
is remarkable less for the extent or breadth over which the limestone has been affected by 
igneous action, than for the strikingly convincing evidence which it affords of the nature of 
the changes induced in the calcareous rock by the series of igneous veins and dykes which 
we have been tracing. The ridge itself, along the side of which the limestone has been 
altered, consists chiefly of a thinly bedded micaceous gneiss. Through the summit, or rather 
on the northwestern flank, which is often abrupt and rugged, there rises a thick granitic dyke 
or vein of very heterogeneous composition, supporting the steeply dipping beds of gneiss, 
whose usual inclination is at an angle of eighty degrees to the southeast. The vein, though 
various in character, and somewhat difficult to describe, owing to the imperfectly developed 
nature of its minerals, and their complete interfusion, may be characterized as consisting, in 
the main, of mica in large excess, quartz, carbonate of lime, felspar, and augite. It contains 
spinelle, sapphire, and green talc, besides several other minerals less distinctly crystallized. 
“ When we consider the highly micaceous character of the adjacent gneiss rock, through 
which the matter of the vein must have passed in reaching the surface, and the abundance of 
the mica, especially of the brilliant golden variety, found so plentifully not only in it, but in 
the adjacent parts of the altered limestone, we cannot resist the impression that a portion of 
the primary strata along the sides of the dyke have been melted and incorporated into it, 
floating, in combination with the other materials, to the surface. 
