34 
GEOLOGi" OF THE SECOND DISTRICT. 
I should have been able to determine this question with greater certainty, if the country had 
been cleared of forests. As it is, there are many impediments to the successful determination 
of the question. Again : If grooves and scratches upon rocks are produced by boulders 
moved along by water, we have another reason for not attributing their origin to the rock in 
Essex ; for we have never observed marks of this kind in an east and west direction : they 
preserve a north and south direction with great constancy in the valleys of the St. Lawrence 
and Champlain. Without pretending, however, to decide the question of the origin of these 
boulders in St. Lawrence county, I would suggest whether it is not more probable that they 
have been brought from Labrador, or some other region far to the north. 
Clay derived from the Hypersthene Rock. —I have already had occasion to remark, that 
this rock changes from a dark smoke grey to a much lighter color, by exposure to the weather. 
Being composed principally of a feldspar, it was not unexpected to find the rock forming, by 
decomposition and disintegration, a substance usually denominated porcelain clay; This re¬ 
sult was realized in the discovery of clay in the valley of the Adirondack above Lake Sand- 
ford. It occurs in a small basin or meadow, through which a small creek flows which rises in 
the adjacent mountain, and which is composed of this rock. The color of this clay is grey; 
it is highly refractory, but not infusible in a porcelain furnace. When burnt for brick, it 
becomes a light yellowish-brown ; hence it appears to contain but little iron. 
This clay, on being moulded and placed in the fire, retains the original-form of the mass, 
and is not liable to fly and crack.. It becomes a valuable article in this region, and quite es¬ 
sential in the construction of furnaces, chimneys, and other purposes in a manufacturing 
establishment. 
Recapitulation. —I have been thus particular in describing the hypersthene rock and its 
principal varieties. This course was called for ; inasrnuch as it had not been regarded as an 
American rock, until after the survey of New-York was in progress. It is unquestionably one 
of the most important primary rocks in the State, whether we take into view its extent, its 
peculiar features, or its productiveness as an iron-bearing rock ; for this reason I will briefly 
recapitulate some of its most striking characters. 
1. The rock is darker colored than the ordinary granites, but weathers to an ash grey. 
2. It is more or less crystalline; as much so as the ordinary granites. 
3. It is composed essentially of only two substances, labradorite and hypersthenethe latter small in proportion 
to the former ; hornblende often takes its place. Epidote, rnica and quartz, so often or constantly present in other 
granites, are very rare in this. 
4. Magnetic oxide of iron is also disseminated very frequently through the mass ; also garnet in grains or small 
masses, scarcely ever in crystals: it is common near the junction of the rock with the ore beds. 
5. The rocks associated are sienite, and some obscure kinds of porphyry, which have been found only in rolled 
masses on the banks of the rivers and streams. 
6. The rock has a jointed structure ; in addition to which, it is often traversed by segregated veins and cracks or 
false joints ; the latter serving to divide'the mass into wedge-form pieces, are finally detached, and form the talus at 
the base of the cliffs. 
7. It is eminently an iron bearing rock; bearing or embracing some of the largest and most important beds and 
veins of the magnetic oxide yet discovered in the United States. 
8. The district of the hypersthene rock is alpine, the mountains being just upon the limit of perpetual frost. 
