14 TACONIC PHYSIOGRAPHY. 
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In 1894 Raphael Pumpelly described the Green Mountains i 
Massachusetts as consisting of three principal structural elements 
"The Green Mountains (Hoosac Mountain); the Taconic Rang* 
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lying several miles to the west ; and. between these, the great valley ; 
but he followed Dana in distinguishing " between a central or axia 
ridge, flanked by an eastern belt extending to the Connecticut, and ji 
western belt extending to the Hudson." The Green Mountain Rang 
is anticlinal and its steep western flank is due to a lofty brow o 
quartzite. The valley has a floor of crystalline limestone with over 
lying island-like ridges of folded schist, sometimes anticlinal bu 
usually synclinal, left by erosion. This limestone valley, whicl 
really extends from Vermont to Alabama, is marked by the fertility 
of its soil, and its limonite ores have long formed the basis of impor 
taut industries. " The Greylock basin of sediment was guarded or 
the north by the large mass of granitoid gneiss of Clarksburg Moun 
tain and on the south by the great body of pre-Cambrian rocks whicl i 
are uoav masked by the Dalton and Windsor quartzite." 
John E. Wolff, in the same work, called attention to the relation 
of topography to structure on Hoosac Mountain. He found that thl 
long crest of the mountain coincides with the axis of a northerly 
pitching anticlinal fold of the central core of gneiss, and that itsi 
profile with gentle slopes and southern-facing bluffs is determined 
by the northerly pitch of the anticline. The east- west trend of the 
valleys in the southern part of the mountain is due to an east- west I 
strike in the sedimentary gneisses. 
In the same volume the writer of the present paper found that thl 
varied surface features of Mount Greylock are due to the interaction' 
of three causes : 
First, the mineralogical character of the rook, presenting minerals more or 
less easily disintegrated by physical or chemical agencies. Second, the internal! 
structure and position of the strata, forming elevations and depressions in the 
mass and determining the surface relations of the different kinds of rock. Third, 
erosion, Glacial, as well as pre-Glacial and post-Glacial, bringing physical 
and chemical agencies to bear upon those irregularities in the form and com- 
position of the surface. * * * The physically and chemically more resistant 
schists form the more elevated portions, also the steeper and more rugged and 
wooded slopes, while the broad, cultivated valleys * * * and the more gently 
undulating portions of the mountain generally correspond to limestone areas. 
[The upper limestone and calcareous schists constitute the high benches of 
arable land, as well as the Notch, which is also anticlinal in structure, and the 
incision between Rounds Rock and Saddle Ball. Professor Dana's surmise 
as to the origin of the north-south part of the Hopper is found to be essentially 
correct. The east-west part of the Hopper and other similar incisions are 
attributed to erosion operating across the folds. The saddle form of the cen- 
tral crest, as seen from the north-northwest, is due to the opposite pitch of the 
a Pumpelly, Raphael, Wolff, J. E., and Dale, T. N., Geology of the Green Mountains 
in Massachusetts : Mon. U. S. Geol. Survey, vol. 23, 1894, pp 5, 6, 21. 
