24 TACONIC PHYSIOGRAPHY. 
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: 
complex in composition and arrangement, embracing gneisses, schist, I 
quartzite, etc. Its special consideration is not within the province of 
this paper, and this applies also to the areas west of Lake Champlain. 
As Glacial and post-Glacial deposits are ignored, the map represents 
approximately the rock surface as modified by all post-Ordovician 
erosion. While the region is all glaciated, the divergence betwed 
the actual rock contours and those of the overlying till, terracj 
gravels, and clay beds is inconsiderable and is confined almost entirely 
to areas below the 1,500-foot level. 
These rocks, viewed as to the degree or mode of their erodibility, 
may be grouped under four designations and the areas underlain by 
them apportioned, respectively, as follows: 
Harder rocks. — Harder rocks (granular, crystalline rocks, an 
gneisses) constitute the westwardly out jutting masses of the Gree! 
Mountain Range and the Rensselaer Plateau, the mass south of Laki 
Champlain along Wood Creek, the Bird Mountain mass in the Taconi 
Range in Rutland County, a small area in Columbia and RensselaeJ 
counties, N. Y., besides several minor quartzite areas — Monume 
Mountain, Rattlesnake Hill, and Stone Hill in Berkshire County, on 
east of Bennington and several on the intermediate range north of 
Dorset Mountain and some east of Lake Champlain in Addiso 
County. 
Rocks of intermediate hardness (schists). — These constitute the 
Taconic Range and its spurs and the masses north and south of Pitts- 
field, and flank the Green Mountain Range at several points in Massa 
chusetts. 
Soluble rocks. — Soluble rocks (limestone, dolomite, and marble 
underlie the Vermont and Berkshire valleys, the minor valleys with! 
the Taconic Range, several strips along Lake Champlain, and small 
areas in Argyle. Greenwich, and Hoosick. These rocks of the Cham- 
plain and Vermont valleys form an almost, if not quite, continuous 
area about the north end of the Taconic Range, There are also 
isolated areas in the Taconic Range in Pawlet, Pownal, and on and 
about the Grey lock mass, and on the Green Mountain Range in Addi- 
son and Rutland counties. 
Rocks disintegrated chiefly by physical processes (shales, unaltered 
grits, and slates). — These underlie the region between the Taconic 
Range and the Hudson, and between that range and the Lake Cham- 
plain limestone area, in places bordering the lake, also between the 
Rensselaer Plateau and the Hudson. For a number of miles north 
and south of the plateau the slates advance several miles eastward 
and the shales also north of it. 
Relation of rock material to surface form. — It will be noticed that 
the harder rocks (Group I) are associated with the plateau type 
and only exceptionally constitute minor hills (Bird Mountain, Stone 
