474 
GEOLOGY OF THE FIRST DISTRICT. 
particles are in a state of at least semifusion, and therefore free to obey their several affinities, 
will readily explain the formation of these insolated crystalline nuclei. The mineral chondro- 
dite contains about fifty-four per cent, of magnesia, with about thirty-eight per cent, of silica, 
besides trivial propprtions of oxide of iron, potash, flu.oric acid, and water. These sugges¬ 
tions respecting the origin of the chondrodite, receive support from the fact that this mineral 
prevails in its usual uniform and moderate proportion through considerable ranges, longitudi¬ 
nally, of the altered limestone, even where not immediately contiguous to the injected veins ; 
while in other parallel zones of the crystalline rock, it is almost wholly absent. Thus, in the 
chain of sparry limestone which stretches at intervals from Sparta towards Lockwood, we find 
it almost constantly present, though never but in moderate quantity. 
“ From several chemical analyses of the sparry, rhombic varieties of the rock containing 
only graphite, and of the white irregularly crystalline kinds enclosing the chondrodite, we 
have still more conclusive evidence tending to settle this interesting point. 
Resuming our progress towards the southwest, we next meet with a succession of de¬ 
tached ridges of the altered sparry limestone, in the valley between the Walkill mountain and 
the primary ridges southwest of Sparta; the latter tract of gneiss separating this belt from 
that previously described. These ridges first appear nearly four miles southwest of Sparta, 
at the extremity of an extensive meadow, and range towards Lockwood. They are four in 
number, the shortest being about one hundred yards long, while the longest exceeds a fourth 
of a mile. Their width is. between two hundred and three hundred feet; they occupy one 
general line; but between their extremities is usually a space of from half a mile to a mile 
of primary strata, whose prevailing dip is towards the southeast, though under circumstances 
of great irregularity. 
“ The white altered limestone of these ridges is rather in the condition of an amorphous 
crystallization, than in the form of rhombic spar. Such is the case at Franklin and Lock- 
wood. It is in fact a coarse granular white marble imbedding many of the rare and beautiful 
crystalline minerals found at Amity and Franklin ; we may mention brucite andgreen spinelle 
of uncommon purity. 
“ Notwithstanding the prodigious extent of igneous action to which the limestone has been 
evidently exposed in these belts, manifested by the width of the space over which a total 
modification of the rock has been effected, we still discern a very distinct stratification, the 
beds dipping steeply towards the southeast. 
“ In the same line with this series, and about one mile and a half further to the southwest, 
occurs another somewhat shorter belt of the altered limestone, a little beyond Lion pond. 
The length throughout which the limestone has been modified, does not exceed two hundred 
or three hundred feet, and the width of the belt is not considerable. The locality is neverthe¬ 
less an interesting one ; for we find well exposed., within a tract not more than a fourth of a 
mile wide, first, the primary strata on the southeast: then the sandstone, F. I.;* next the blue 
* The Potsdam sandstone of the GeologiQal Reports of New-Yprk. 
