52 
ROCKS OLDER THAN THE TACONIC SYSTEM. 
Hoosic or Green mountain on the east. The succession of this lower division is represented 
by an actual section extending from Glen’s falls five miles northeast, or to the primary 
upon which the Potsdam sandstone rests. 
rig:, l. 
a. Granite; b. Potsdam sandstone; c. Calciferous sandstone; d. Trenton limestone; e. Black marble, extending 
towards the river. 
The gorge at this place is not sufficiently deep to expose the Potsdam sandstone, but the 
succession is well exhibited in passing over the country in the direction stated above. The 
Utica slate at the falls has been mostly destroyed by denudation ; but it appears both above 
and below, upon the river banks, with its characteristic fossils, succeeding the Trenton 
limestone. 
The point to be shown, is that the lower division of the New-York system reposes upon 
some of the members of the Taconic system ; that is, to show by actual superposition that 
the former rests upon the latter. I trust I shall be able thus to do: not only to point out 
where the two systems approach each other so closely that there is but little space inter¬ 
vening between them, hut where the finger may be placed directly upon the line of 
demarkation; the one being the inferior and unconformable, and the other the superior. 
This great fact being shown, its bearing on American geology is not confined to one or 
two subjects, as metamorphism and age; but it is also important as furnishing a base from 
which may be formed a general nomenclature of sedimentary rocks. At any rate, it is a 
point to be established before a nomenclature can be devised, that shall express the order 
in which the series follow each other, and the designations proper to apply to them. 
§ 4. Rocks below and older than those constituting the taconic system. 
In Massachusetts and Vermont, as well as in New-York, what has been usually deno¬ 
minated the Primary range skirts the Taconic system upon the east, and forms with it 
parallel belts of low mountain ridges, which unitedly form the Green mountains. Different 
portions have received different names; as Hoosic mountain, immediately east of Adams 
in Berkshire (Massachusetts); and Mansfield mountain, to the east of Burlington (Vermont). 
The Taconic range is parallel with the main ranges constituting the Green mountains, 
and is a few miles only to the west. The ridge dividing New-York from Massachusetts is 
the one to which this name was originally given. The ranges are, however, connected 
by spurs, though not so intimately as to destroy the integrity of either, and make it 
necessary to merge them both in one main range. The name (xreen mountains is a more 
