44 TACONIC PHYSIOGRAPHY. 
the highest part of the edge of the plateau, is TOO feet. At a 1 
a half mile east of the edge the cut bifurcates into longitudinal o 
At this place a small stream, the Poesten Kill, is cutting the limb 
minor anticline before flowing along the strike. 
The four small parallel east-west cuts in the schist mass eas 
Granville are very probably related to east-Avest joints. One of 
most instructive of such cuts is the Hopper, on Mount Greylock 
map, Pis. X, ^4, and XI). This is a 1,500-foot-deep norths 
southeast incision, which extends completely across the western i 
cline of the schist mass. The cut then opens into the NNE.-S£" 
longitudinal hollow referred to by Dana, along an anticlinal a 
The eastern wall of this hollow is cut into by six transverse mourn 
torrents, which are extending the work of the first one and attach 
the central syncline of the mass. The most southerly of the brain 
of Hopper Brook describes a peculiar curve in its descent of 1 
feet, its upper and lower courses being parallel to the strike, but 
middle course across it. A similar curve is described by a ravine 
the north side of the Greylock mass. As may be seen by PI. X, .4, 
amount of material removed from the transverse incision alone 
inverted, would make a pyramid 1,500 feet high with a base a i 
square. 
The most complete amphitheater in the Taconic region is Skin 
Hollow, on the eastern side of Mount Equinox, in Manchester I 
PI. X, B). But the map does not do full justice to the ma them at 
regularity of the excavation. It is across the strike, although 
inclination of the beds is slight. The depth from the crest to w| 
may be called the back of the hollow or the bottom of the stee : 
>lope is from 1,000 to 1,700 feet, and from that point to the moJ 
the descent is 500 feet and the distance 1 mile. The spurs on 
north and south are from 900 to 1,000 feet above the mouth, 
shown on PL I, limestone rises to the 2,500-foot contour in the lioll 
-o that the amount of material eroded would, if inverted, makkl 
conical mass about 1,550 feet high with a base 1 mile in diameter, i j! 
of this cone the lower 550 feet would be siliceous (schist), while 
upper 1,000 feet would be soluble rock (marble). The very sa j 
metrical character of this amphitheater suggests the bare possibiiil 
that a local glacier may have had something to do with its sculptu j 
\Ahere the brooks reach the soluble rocks chemical action coif 
strongly into play, and miniature canyons of white marble soi 1 
times occur, as at the " Natural Bridge " near North Adams, wli 
both the axis of a fold and the strike of several systems of joi : 
" Dana, James D., Am. Jour. Sci., 3d ser., vol. 6, 1873, p. 273. 
6 See Tarr, Ralph S., Glaciation of Mount Ktaadn, Maine : Bull. Geol. Soc. Am., ij 
11, 1900, pp. 433-448 and pis. 33, 34. Also Hitchcock, Charles H., New England 1 
glaciers : Ibid., vol. 7, 1896. Emerson, B. K., Glacial cirques and rock terraces 
Mount Toby, Massachusetts : Science, vol. 17, p. 224. 
