192 J. D. Dana— Age of the Green Mountains, 
(3) The occurrence of unconformable i ai Silurian rocks 
within the limits of the region or on its bor 
(4) The spr tuto of an individual among > saree ins 
1. The extent to which the tigen belt 1s a known region as re- 
gards geological age.—The fac on this point are presented in 
the writer's former papers,* and need not be here repeated. 
They establish (1) by means fs ate the discoveries of Wing 
and others in Vermont, and of Dale, Dwight and the writer in 
Dutchess County, N. Y., and (2) By the conformability of the strata, 
the Lower Silurian age ‘of the Taconic schists and of the asso- 
ciated limestones and schists, eastward to the easternmost of the 
limestone bands, and westward through Dutchess County, 
ew York, to (and somewhat beyond) the Hudson River. 
Through their conformability, these strata show that all are one 
in system of dislocation and one in epoch of mountain-making ; 
that the several Lower Silurian formations, from the Hudson 
River group to the Primordial, are involved in one system of 
Vermont, 15 to 20 miles, or two-fifths of the width of the 
State; in Massachusetts, 15 to 20 foiled! in Connecticut, 12 to 
15 miles; in Dutchess County, N. Y., west of Connecticut, 23 
to 25 miles, reckoning to the Hudson River. 
The width for Western Connecticut and Dutchess County 
Dutchess County, in Columbia and Rensselaer Counties, N. Y., 
the rocks are a continuation of the slates of Dutchess County, 
and are conformable to the Taconic, according to Mather and 
Emmons, and hence they belong to the same : system. Conse- 
chusetts is 40 miles, or, again, half the distance from the Hud- 
son to the Connecticut. e rocks are also Lower Silurian in 
Washington County, up to ” Whitehall, as represented in the 
a oslton maps of Hall and Logan; and in the northern balf 
ermont, to its northern boundary 
t thus appears, that, of the mass “Or land which topograph- 
sla belongs to the Green Mountain range, that part ‘which 
is already proved to be Lower Silurian in age, and of one geo 
* This Journal, IIT, v, vi, 1873, xiii (Wing’s discoveries), xiv, 1877, xvii, 1879. 
The conformability Pi tooeg the Taconic schists and the ‘sao rg limestone 
I have observed at various localities in Vermont, Massachusetts, Connecticut and 
New York of the localities on the west side of the range and rest on the 
eas d the same limestone and the schists (including mica schists 
and gneiss) and quartzyte to ward also at several localities in Vermont, 
Massachusetts and Connecticut, so that the fact cannot nghtly be question ned. 
The discoveries “of fossils near Newburgh, west of the Budeon, by Whitfield and 
Dwight, are additional evidence as to the relation of the 
