75 



fusion, and, therefore, free to obey their several affinities, will 

 readily explain the formation of these insulated crystalline nuclei. 

 The mineral condrodiie contains about 54 per cent, of magnesia, 

 with about 38 per cent, of silica, besides trivial proportions 

 of oxide of iron, potash, fluaiic acid, and water. These sugges- 

 tions, respecting the origin of the condrodiie, receive support from 

 the fact, that this mineral prevails in its usual uniform and mode- 

 rate proportion through considerable ranges, longitudinally, 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 condrodite, 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 detached ridges of the altered sparry lime- 

 stone, in the valley between the Wallkill 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 ex- 

 tremity of an extensive meadowy 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 circum- 

 stances 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 Lockwood. 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 and gre.e7i spinelle of uncommon purity. 



