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Unformatted text preview: cial
scour, striations, and crescentic
Bedrock - Shawangunk
Formation, cross-bedding, and
joints. OAD N TO
MONUMENT park on gravel STOP 1 park
23 crossbedding Stop 1 freeze
thaw Explanation - The overall streamlined and smoothed rock surface,
faint striations, and crescentic marks are products of glacial erosion.
The scratches and crescent-shaped marks on the outcrop east of
Scenic Drive, show that the ice sheet (Kittatinny Valley lobe) flowed
S 70o W. Several angular to subangular boulders of conglomerate,
glacially transported from nearby locations, lie on the scoured rock
surface. The many-sided pattern outlined by vegetation on the
rock surface (fig. 14) follows joints and fractures in the bedrock.
These features gradually widen over time by the action of freezing
water, and root growth, eventually they fill with rock fragments
that form a thin soil. The expansion of ice also breaks the rock
apart along bedding surfaces as shown by the upward movement
and change in position of some joint blocks (figure 14). 1 foot polygonal outline of
joint-block boulder Figure 14. Stop 1: Outcrop of the Shawangunk Formation showing many joints
and joint-block boulders. The Shawangunk Formation here consists of thin-to- thick layers
of quartzite and conglomerate that slope gently to the southeast,
forming the eastern limb of an anticline. Cross-bedding, visible on
parts of the outcrop, consists of thin, stacked, and curved layers
(fig. 5). The orientation of cross bedding shows the ancient river
that laid down these deposits flowed in a northwesterly direction.
Excellent examples of cross-beds are exposed on the northwest
side of Scenic Drive on the slope just below the road surface.
25 Other Occurrences - Evidence of glacial scour, striations, and
cresentic marks are found throughout the park where bedrock
is exposed. In some places weathering has roughened the rock
surface, obscuring these markings. The effects of such weathering
may be seen wherever bedrock is exposed, and cross-bedding can
generally be observed at most of the...
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