This preview shows page 1. Sign up to view the full content.
Unformatted text preview: form by compressive force, similar to pushing two ends
of a piece of paper together. The arches and troughs that form
are called anticlines and synclines respectively. Fold magnitude
varies in each formation, but in the park it is on the order of
several hundred feet (fig. 6). Generally, folds cannot be seen at
an individual bedrock outcrop. One needs to walk across the rock
and note the slow change in the dip of the beds from southeast to
A fault is a fracture or group of fractures in rock where one
side has moved past the other. Such breaks form when rock is
squeezed or pulled apart. An offset of sedimentary layering marks
the location of a fault and helps to determine the rock’s movement
direction. Faults that parallel layering are harder to discern. A
fault commonly exhibits linear grooves that show the direction of
High Point Member
unconformity bedding anticline 2000 FEET 1000
-1000 Sb Lake Marcia
Ss Omh anticline syncline Ss land
surface 1000 Ss Omh Omh SEA
-1000 1 mile -2000 2000 FEET Sb -2000 Figure 6. Regional crosssection through Lake Marcia from the northwest (left) to
the southeast (right). The view, taken from the Lake Marcia beach, faces north
toward the monument. motion. These grooves form where bumps on the fault surface
slide past and gouge the opposing rock surface. Quartz veins are
also common in faults and their alignment is similar to that of the
grooves described above. Faults cut the three rock formations in
the park; all are small, have minor offsets, and are no longer active.
They are most common in the brittle rocks of the Shawangunk
Joints are the most common structural feature in rocks (fig. 7).
They are fractures, but unlike faults, they show no evidence of
movement parallel to their common surface. Joints form where
pulling or pushing forces caused the rock to break. Joints may
cut across a whole outcrop or only an individual bed,...
View Full Document