876 J. D. Dana—Hudson River Age of the Taconic Schists. 
RN Rp OS 
made observations toward the same end, and also widely, over 
Dutchess and Westchester Counties, New York. The work is 
still far from finished. But the discoveries by Mr. Dale at 
Poughkeepsie throw so much light on the general question at 
issue—the age of the Taconic schists, when they are connected 
with the facts already learned, that I here anticipate my fuller 
memoir by a brief statement of the facts and their bearing. 
1. On tar Hupson River Ace or THE Taconic ScHIsts. 4 
(1.) The discovery, by Mr. A. W1NG, of Trenton fossils, Zr 
nucleus concentricus and other species, in beds of the crystalline 
limestone formation of Vermont that directly adjoin and under- 
lie conformably the slates of the north-and-south Taconic belt, 
has established the fact that these Vermont slates are of the age 
of the Upper Trenton or the Hudson River group; and the fact 
_ that this ‘hy i 
tains and becoming the limestone of Copake and Hillsdale on 
the west—affords scarcely less positive proof that these Berk- 
shire Taconic slates also, the original typical Taconic slates of 
Emmons long supposed to be Cambrian or pre-Silurian, are 
of Hudson River age. 
This conclusion loses nothing of its certainty in consequence 
of the fact of a change in the schists of the belt from argil- 
laceous schists at the north (one source of ‘the roofing-slate 
ey of Vermont), to hydromica, chloritic and garnetiferous 
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16 of his New York Geological Report (1843), across the 
“mountains fifteen miles farther south, represents the limestone 
of Salisbury as dipping westward beneath the slates while those 
of the west dip eastward, as they do elsewhere on that side of 
the mountains. Further; my own recent observations in Nor- 
isbury, within three miles of the Massachusetts line, 
confirm those which I made just north in Western Sheffield; 
