FAULT SCARPS. 
45 
Hve determined the course of the brook. The development of this 
qnyon is also due to the mechanical action of bowlders of granite and 
jjartzite rotated upon the marble. 
[(Some ravines, however, have a very different history from these. 
|)r instance, in the eastern edge of Pittsford, Vt., is a notch known 
lally as " The Gorge " (PL IX, B), which is from 100 to 800 feet 
Hep, TO feet wide at the bottom, and from 500 to 1,000 feet long. It 
fj choked below with great angular blocks of quartzite which have 
jjjllen from the sides. At the north it ends abruptly in a mass of 
lecciated quartzite, and the western side is similarly brecciated. 
■either glaciation nor the bedding can well account for this notch, 
U both cross it, the stria?, which run S. 15° E., making an angle of 
6° with its sides. But as it is in exact line with the Pine Hill over- 
jirust on the south," and as breccias are usual about faults, its origin 
lay be attributed to the fault. Ice Glen in Stockbridge, Mass., 
lay be likewise due to a fault or to a parting along a plane of frac- 
J80Q4—---' 
> 
X 
s 
s 
s 
/ 
§8^r5>^ *~"~~ "'' 
/ 
^^^^S 
=^— *^^ 
-* , ^ -^^-— J ^ = ^ ±=^^-— 
Scale „_ x . 
500 feet /. 

j Fig. 3. — Section from the top of Dorset Mountain, on left, to Danby Hill, in Danby. 
It., showing the eroded fault scarp. The lowest rock is quartzite, then marble with 
,olomite, lastly schist. 
ure. A small canyon in Poultney has already been referred to as 
}ue to the erosion of a basaltic dike in slate h (pp. IT, 25). 
FAULT SCARPS. 
The conspicuous quartzite cliffs on the east and west sides of Monu- 
nent Mountain in Great Barrington are fault scarps (fig. 2). c The 
sast-west face of Dorset Mountain, already referred to on page 15, is 
:eally an eroded fault scarp (PI. II, and fig. 3). The north-south 
section (fig. 3) shows that the mass of limestone and schist eroded on 
the upthrow side of the fault was about 3,000 feet thick and not less 
than 2 miles long. About 22 miles north-northwest of the northern 
<• See Fourteenth Ann. Rept. U. S. Geol. Survey, pt. 2. 1804, pp. 548, 549, and fig. 64. 
'' See diagram, Nineteenth Ann. Rept. U. S. Geol. Survey, pt. 3. 1809, fig. 12, p. 222. 
<' See also Fourteenth Ann. Rept. U. S. Geol. Survey, pt. 2, 1894, 563, fig. 71. 
