DISTRIBUTION OF THE HYPERSTHENE IN BOULDERS. 
33 
Hypersthene rock occupies, therefore, a triangular area, which is confined almost wholly to 
the county of Essex; in fact, it would not be far from the truth to consider all of this county 
as composed of this material, excepting a belt a few miles in width along the shore of the lake, 
which is gneiss and hornblende, and rocks of the Champlain group composing a part of the 
transition class. The width of those rocks diminishes towards the north. In travelling west 
from Port Henry to West Moriah, the rock becomes decidedly the hypersthene rock in about 
nine miles ; while from the lake at Westport, we fall upon the rock in three or four miles. 
The passage from gneiss to hypersthene is marked by gradual changes. I have not been able 
to find a line which marks, with any degree of distinctness, the place where the gneiss on the 
one side ends, and hypersthene rock on the other commences. Viewed in the extremes, the 
two rocks are widely different; as they approach each other, the materials of which each are 
composed become so incorporated, that it is difficult to determine to which mass the interme¬ 
diate portion belongs. 
The area which is occupied by this rock is the most mountainous district in the State, the 
highest mountain ranking only second in height to any in the United States. 
Distribution of the Boulders of this Rock .—A rock whose locality may be so clearly de¬ 
fined, and whose characters are so distinct, becomes one of the best rocks for observation on 
the distribution of its boulders. I have, therefore, been careful to search for them, wherever my 
pursuits have called me since the commencement of the survey. The result of my observations 
is, that they are distributed in lines nearly south of the present rock in the county of Essex. 
Thus they are found abundantly in the valley of the Mohawk ; at Amsterdam, they are very 
common ; and still farther south, in the county of Orange, boulders of this rock attracted the 
attention of mineralogists at a very early day, from their containing tolerable specimens of 
opalescent feldspar. This county appears to be the limit of their distribution in this direction. 
Although the lines of distribution appear as stated, yet there are important and interesting 
exceptions. On Lake Ontario, nearly west of the great hypersthene tract, boulders of hypers¬ 
thene rock are quite common ; also on the St. Lawrence in the vicinity of Ogdensburgh. In 
relation to this line of boulders, however, it is not possible to determine satisfactorily their 
origin ; and I am disposed to assign them an origin still farther north, rather than to the New- 
York formation. There is a very good reason for this opinion ; it is this, there is no line of 
boulders by which we can trace them to the region of this rock in Essex county, but they ap¬ 
pear to be arranged on the lake and river in a direction north and south ; and though we may 
find a few twenty miles east, they become more rare the nearer we approach the table land of 
the Racket. Those which are found upon the lake and river, however, cannot be distinguished 
from those in the valley of the Mohawk ; they belong to the same rock : but if they originated 
in the Essex hypersthene rock, it seems very probable we should be able to trace them back 
to their source.* 
♦ The diluvial marks upon the hypersthene rock are nearly north and south, and an interesting example of them may be seen 
in the valley of the Adirondack river; they pass over one of the large beds of magnetic oxide of iron, and were finely exhibited 
by the recent removal of the soil. This locality is nearly 2000 feet above Lake Champlain. 
Geol. 2d Dist. 5 
