HORNBLENDE. 
79 
sion of the walls, and then narrow again by pinching in, as it is termed, when the vein loses 
width. I shall have farther occasion to speak of this subject, when I take up for considera¬ 
tion the iron ores, and a few other substances which have been found in veins in this rock ; 
and it is sufficient that I remark in this place, that it is a valuable rock for mining, in conse¬ 
quence of the permanence of the mineral matter, whether it is pursued downwards, or in the 
direction of the strike of its veins. Besides this, I may state, that it is by no means an 
unproductive rock, as will be seen in the sequel. It is true, however, that there are quite 
large tracts which appear to be entirely destitute of metalliferous veins. Such is the case 
with a large part of Hamilton county, which is composed mostly of gneiss ; and there appears 
to be but few instances in which even stony matter occurs in veins, or, in other words, dykes 
appear to be less frequent than in Essex, where mineral veins are quite common. 
Imbedded Minerals. 
Gneiss, in the Northern District, cannot be said to be prolific in simple minerals. Its con¬ 
nection with iron ore, limestone, serpentine, and their particular associates, have been stated 
in detail. Considered independent of these rocks, it is in truth barren of interesting minerals. 
Indifferent crystals of tourmaline, garnet, hornblende and pyroxene, are not uncommon; but 
these minerals do not occur in perfection, except where the gneiss is associated with lime¬ 
stone, quartz or granite. Zircon and phosphate of lime, in small crystals, occur not far from 
Clintonville. Limonite, or the brown peroxide of iron, and graphite, near Ticonderoga; 
sulphuret of iron, diffused through the rock in Canton, and in numerous places ; one of the 
oxides of manganese, crystals of quartz, eupyrchroite, epidote and pyroxene, at Crown Point; 
green fluor spar, and crystals of calcareous spar, at the Arnold ore bed in Peru, constitute the 
greater part of the simple imbedded minerals in the gneiss of the northern counties of New- 
York. 
2. Hornblende. 
There are no extensive masses of this rock in the Second Geological District. It forms 
ledges from twenty-five to eighty rods in length, in many places, but is not continuous over 
large areas. Sometimes it forms a compound with gneiss, a mixture in which hornblende 
takes the place of mica, forming a dark colored rock, which appears much like sienite, ex¬ 
cepting that it does not break into tabular masses. 
This rock is of so little consequence, that I have merely introduced it for the purpose of 
saying that it is one of the rocks of this district. At Port Henry, it forms a part of the hill 
immediately in front of the landing; and is here, as usual, connected with primitive lime¬ 
stone. Some of the beds and veins of the magnetic oxide of iron are in this rock; and so 
far as it is considered as a mining rock, it is as productive as gneiss. The ores of iron in 
this rock are more pyritous, and tougher or more difficult to break, than in granite or gneiss. 
Thus, at Crag Harbor near Port Henry, the ore is extremely difficult to break and prepare 
