LOWER PALEOZOIC. 217 
the rocks included within it in 1842.* The gneiss is represented 
on the extreme east and the " Taconic slate" on the extreme west 
and the "shales of the Champlain group " as resting unconforra- 
ably on the " Taconic slate." This section includes all the strata 
of the "Taconic System," as then known to Dr. Emmons, and 
agrees with the description, in the accompanying text, of the 
rocks of the System. f 
. As is mentioned in the 1st reason given for rejecting the name 
Taconic, there is not a known stratum of rock in the Taconic 
range that is of the geologic age assigned to it by Dr. Emmons. 
In 1844 he incorporated a great series of slates and shales 
belonging to another geologic system by extending his sections 
across the western belt of the Hudson Terrane, that limited the 
section of 1842, and on the west to the next line of outcrop of 
Lower Silurian rocks. This addition gave the opportunity to 
separate oif the "Upper Taconic" in 1856. I have shown that 
all his reasons for calling this series pre-Potsdam were based on 
errors of stratigraphy ; and that it was a fortunate happening that 
any portion of the " Upper Taconic " rocks occur where he 
placed them in his stratigraphic scheme. Even if there were no 
errors to vitiate Dr. Emmons's argument for the pre-Potsdam 
position of the " Upper Taconic," that portion of his system 
could not retain the name "Taconic;" for it belongs to a dif- 
ferent stratigraphic system from that to which the strata of the 
Taconic range belong, and to which he gave the name " Taconic." 
The following tabulation of the successive phases of the Ta- 
conic system viewed in the light of present facts is instructive. 
It was proposed in a letter from Professor Dana to the writer : 
Phase I., 1842 
' "Taconic System," .... 
True order begins. 
6. 
Stockbridge limestone, . 
II. Lower Silurian limestone. 
5, 
j Magnesian slate of Gray lock, 
III. Hudson slate. 
i Granular quartz, .... 
I. Cambrian. 
* . 
4. 
Limestone, ..... 
II. Lower Silurian limestone. 
3. 
Magnesian slate of Taconic moun- 
tains, 
III. Hudson slate. 
2. 
Sparry limestone, .... 
II. Lower Silurian limestone. 
. 1. 
Taconic slate, .... 
III. Hudson slate. 
* Geol. N. Y., pt. 2, p. 145, 
Fig. 46, 1842. 
t Loo. cit., pp. 144, 145. 
