222 
GEOLOGY OF THE SECOND DISTRICT. 
less common; and when it appears, it is more in the form of narrow dykes, than where it 
appears upon the outsides of this formation. 
But I propose to state more definitely the boundaries and extent of this important rock. 
Its northern termination is Trembleau point on Lake Champlain, near Port Kent. From this 
point, the eastern boundary line extends a little west of south, through the western part of the 
town of Essex, and about half way between Westport and Elizabethtown, through Moriah 
and the west corner of Schroon; passing on through Minerva, the northeast corner of 
Hamilton, and the southeast corner of Franklin county ; and then passing northeast through 
Wilmington, and east to Trembleau point. The lines, as thus laid down, may include some 
other rocks along either of the borders, and may also cross the hypersthene in others. The 
general extent, position and boundaries, however, are as accurate as it is possible to give in 
a country, the larger portion of which is entirely wooded, and in which surveys have been 
very imperfectly conducted and performed. To New-York, this is an important tract; as it 
embraces the great iron region, which is surpassed by none either in this country or any other, 
in the amount of ore, the quality of iron it furnishes, or in the facilities for reducing it. 
Hypersthene rock is composed mainly of Labrador feldspar, or lahradorite, as it is termed. 
It is not a rock in which hypersthene abounds, as its name seems to imply, though it is more 
abundant than appears in the fresh fracture : it only comes distinctly out by weathering ; its 
lustre of bronze then first appears ; but before this change, it has much the appearance of 
hornblende, or some of the dark varieties of feldspar. The rock is, however, mostly Labrador 
feldspar. It is not easy to describe it so as to create an image of the rock itself in the mind. 
It is, however, a very distinct mass, and is easily recognized after an acquaintance has been 
formed with it. 
This rock always forms steep and precipitous hills and mountains, with a tendency to 
conical summits and sharp rounded peaks ; but there is no regularity, as I have been able to 
observe, in the steepness of the sides, as is the case when the mountain is underlaid or com¬ 
posed of stratified rocks. We certainly find perpendicular precipices on all sides ; and should 
there be found a greater steepness on one face, as the eastern, I should be disposed to consider 
it as accidental, rather than as the effect of a law. In a region composed of stratified rocks, 
if an uplift takes place so as to produce a fracture, the steepest side is invariably that in which 
the fracture is made. 
The conical shape of the mountains formed of this rock, has led to the popular opinion 
that the region is volcanic ; and accounts are often related, of lights being seen, explosions 
heard, and sulphur smelt. But in no part of the Adirondack group is there a trace of a crater, 
or any sign distinctly volcanic, either ancient or modern, except in the trap dykes which are 
so common throughout the whole territory. It is, however, a curious fact, that Mount Etna 
is composed of the same variety of rock, namely, lahradorite ; though I am not prepared to 
say that this belongs to a volcanic district, any more than granite or gneiss. 
It is a question which has often forced itself upon my attention, whether the Adirondacks 
are an older or newer system of mountains than those of New-England 1 In reaching the 
