J. D, Dana—Age of the Green Mountains. 191 
Art, XXTV.—WNote on the Age of the Green Mountains; by 
JAMES D, Dawa. 
HavinG in the new edition of my Geology, as in the pre- 
ceding, referred the epoch of the formation of the Green 
Mountains, that is, of the folding, upturning and crystalliza- 
tion of its rocks, to the close of the Lower Silurian, I here pre- 
sent a fuller statement of my reasons for this conclusion. A 
further study of the stratigraphy of the eastern part of the 
region is required to establish its correctness beyond question ; 
but I believe that the following facts and considerations will 
be found to be strongly in its favor. 
_ By the term Green Mountains, I mean the swell of land with 
its ridges, about N. 16° EB. in trend, which lies between the 
Connecticut River on one side, and Lake Champlain and Hud- 
son River on the other, and reaching in the south to New York 
Island. All the rocks of the area thus bounded are not refer- 
able genetically to the range; for it is well known that the 
“Highland ” region of Archean rocks extends over the most 
of Putnam County, New York, and the southern border of 
Dutchess County ; and that rocks of the same age constitute 
areas to the east of north of this Highland region, in Connec- 
“cut, and also farther north in Massachusetts and Vermont. 
ese Archean areas introduce difficulties into the geology of 
Western New England. But the Taconic range and the asso- 
staphy ; and by working from it, the difficulties will quite surely 
be ultimately surmounted. For the sake of the present dis- 
cussion, the Green Mountain region may be regarded as con- 
sisting of (1) a Western section, which includes the Taconic 
Tange or belt, and the associated bands of limestone, together 
with conformable formations of slate and schists; (2) a Central 
mountain section, separately distinguishable only in Vermont ; 
and (3) an Eastern section. The mountain section in Vermont 
Contains the highest summits of the Green Mountains, and is 
the part to which the name was given. In Massachusetts, the 
highest peaks are in the more western Taconic range ; but still 
the greatest mean height lies south by west of the mountain 
t of Vermont. ' 
In the following pages, the evidence reviewed is arranged 
under the followin bende 
e extent to which the Western belt is a Anown region 
a8 regards geological age. 
) The relations in rocks and stratification between the 
Western belt and those east of it. 
