CHAMPLAIN DIVISION. 
373 
and at Lawrence’s quarries opposite Wilbur, underlying the limestones of the Helderberg 
division unconformably (PI. 24, fig. 1). They form the banks of the Walkill at Eddyville 
and Dashville ; the Shawangunk and Marlborough mountains, and Huzzy hill; the banks of 
the Hudson where the rocks are exposed from the mouth of the Walkill to the Highlands on 
the south, and to Baker’s falls on the north. 
These rocks dip to the east-southeast, with some local exceptions, at a very high angle. 
The slate rocks form the mass of the strata from Marlborough five miles west towards 
Pleasant-valley, some of which are black, and more or less loaded with carbon. The black¬ 
ness of some of these strata, and the impressions of plants (graptolites) contained in them, 
have led to excavations for coal; but, as might be supposed, none has been discovered. The 
Marlborough mountain, or Breakneck hill, as it is called, is a coarsely stratified grit rock, 
containing in some places some carbonate of lime. The rock is not coarse-grained, but is 
hard, and at a little distance, and even near, has the general aspect of a primary rock. Slate, 
interstratified with coarser grits, succeeds on the west of Marlborough mountain, and extends 
to Pleasant-valley. 
Between Rosendale and Dashville, the grits are beautifully exposed on the banks of the 
Walkill, and particularly opposite the bridge across the Walkill, and between that place and 
Dashville. They form strata one and a half to five feet thick, of solid greywacke as it has 
been called, with thin layers of shale between. These rocks are intersected by two systems 
of joints in nearly vertical planes, ranging N. 20° W. and N. 70° E. These seams or joints 
make faces to the blocks nearly as regular and smooth as if they had been sawed. The falls 
at Dashville exhibit a fine section of some of these rocks, and a fault and derangement may 
here be seen (Vide PI. 7, fig. 7). The strata are nearly horizontal above the fall; but at a 
break and fissure at the foot of the fall, the contortion begins, as represented on the plate 
above mentioned. On the right bank of the stream, the whole inverted arch may be traced, 
as represented on PI. 7, fig. 8. The strata have been cracked, and opened on the extrados of 
the curves,, as if they had been consolidated before they were bent, and had cracked as re¬ 
presented on PL 7, fig. 8, or more distinctly on PL 7, fig. 8'. These cracks have since been 
filled with quartz and calcareous spar. The hill east of Dashville shows a part of the re¬ 
versed arch. Drusy quartz and fragments of anthracite were observed in the grit rocks near 
the bridge, a quarter of a mile above Dashville, and some few fossil shells. 
Marlborough mountain, which extends from Orange county and terminates in Huzzy hill, 
in the angle between the junction of the Hudson and Walkill rivers, is composed of the grits 
and slates of this group. The strata are inclined at a high angle, dipping generally thirty to 
eighty degrees to the east-southeast. This mountain ranges nearly parallel to the Hudson, 
and has an elevation in some places eight hundred to one thousand one hundred feet. This 
range of hills scarcely deserves the name of a mountain, but is called the Marlborough moun¬ 
tain. It is on one of the breaks, or lines of upheaving action, parallel to the Hudson river 
anticlinal axis. 
A brecciated rock, somewhat peculiar in character, occurs in the Marlborough mountain in 
