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GEOLOGY OF THE SECOND DISTRICT. 
CHAPTER VIII. 
Rocks composing the Taconic system; order of superposition; general strike and dip .— 
Liability to mistake some of the slates and limestones for those which belong to other 
systems. 
The number of rocks which compose the Taconic system is quite limited; this is an 
important feature, which is not to be lost sight of. It does not, however, follow that it is 
necessarily thin; on the contrary, it is remarkably thick, and hence becomes of more impor¬ 
tance than appears from a simple statement of the number of rocks of which it is composed. 
As a whole, we find granular quartz, slate and limestone to form the entire system. But it 
is to be remarked, that it is necessary to take cognizance of two kinds of slate and two of 
limestone ; for although there are many points of resemblance in each of the two rocks respec¬ 
tively, still their position and lithological differences, though small, require their separation. 
The full enumeration is as follows : 
1. A coarse granular limestone of various colors, which I have demoninated Stockbridge limestone, taking its name 
from a well-known locality, one which has furnished to different parts of the Union a large proportion of the white and 
clouded marbles which have been so extensively employed for building and other purposes in construction. 
2. Granular quartz rock, generally fine-grained, in firm tough crystalline masses of a brown color, but sometimes white, 
granular and friable. 
3. Slate, which for distinction I have denominated Magnesian slate, from its containing magnesia, a fact which is 
distinctly indicated by the soft feel peculiar to rocks when this earth forms a constituent part. 
4. Sparry liniestoTie, generally known as the sparry limerock. 
5. A slate, which I have named Taconic slate, and which is found at the western base of the Taconic range. It lies 
adjacent to the Lorrain or Hudson river shales, some varieties of which it resembles. In composition, it contains more 
alumine and less magnesia than the magnesian slates. 
In addition to the above rocks, there is sometimes a slate of a dark color, and quite sili¬ 
ceous, in the granular quartz. This appears less constant, and may be considered as a slaty 
quartz, or variety of this rock. There are several deposits, important in themselves, which 
strictly belong to this system: the hematitic iron ores, associated sometimes with carbonate 
of iron, and the black oxide of manganese. Subordinate to the rocks, we find milky quartz 
and chlorite, with carbonate and oxide of iron in the magnesian slate. 
The following section, extending from Petersbugh, Rensselaer county, to Adams in Massa¬ 
chusetts, embraces all the rocks in this system. Its direction is nearly east and west, or 
perpendicular to the strike of the system over which it passes: 
