992 The Crystalline Rocks of the Northwest. (October, 
below the New York system, and separating it from the “primary,” 
as by doubt as to which and how many of these sub-Silurian strata 
are to be included in the designation of Taconic. Having now 
however, given the subject very careful consideration, I am ready 
to state my very positive conviction that Dr. Emmons was essen- 
tially right, and that the Taconic group will have to be recognized 
by geologists and adopted in the literature of American geology. 
Dr. Emmons, in 1842, issued the first that appeared of the vol- 
umes of the final report of the New York survey. In that volume 
he formally sets forth the Taconic system, although, as he admits, 
in an imperfect manner, the area in which the rocks exist not be- 
ing in his (the second) district. In this first presentation of the 
system he extended it geographically too far east, and unfortu- 
nately chose a name for it which is appropriate only to a part of 
that eastward extension. We are indebted to the researches of 
several volunteer geologists, Wing, Dana, Dale, Dwight, for the 
disentanglement of the overlying Hudson River rocks from the 
true Taconic rocks, and the demonstration of the incorrectness of 
Dr. Emmons’ eastward extension of his system in southern ve 
mont. Dr. Emmons’ claim, however, in all its essential points, 
remains intact. This consists in the existence of a series of sedi 
mentary deposits, largely metamorphic, below the Potsdam sand- 
stone, and separating the Potsdam from the crystalline rocks 
known as “primary” in an orderly chronological scheme. 
In his report on the agriculture of New York, issued four et 
after that on the geology of the second district, he makes mor 
definite and convincing statements, going over the whole subject 
de novo. He gives diagrams showing the Taconic slates lying 
below the Calciferous sandrock unconformably, at Whitehall, 1 
Washington county, a region that had been colored by M 
and Hall on their geological maps as Hudson River, and lying 
the general area described by Emmons as Tacouic. He gives o 
also from the hills of Greenbush, opposite Albany, not far an 
the locality in which Mr. Ford has since discovered primordi i 
fossils, where he also shows the Calciferous lying unconformab y 
upon the Taconic, the former being fossiliferous. He also describes 
_ the Hudson River slates as lying unconformably on the T 
a fact which cannot be called in question since the recent peer 
eries of Wing, Dale, and Dwight, and the stratigraphic investig® 
tions of Daria. In fact, the investigations of these geologists, A 
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