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Unformatted text preview: park show that the glacier flowed S70oW to due west.
These features were made near the edge of the Kittatinny Valley
ice lobe when the front of the ice was retreating. It is likely that
southerly-oriented striations, made earlier when the ice was much
thicker and its margin far south of High Point, were subsequently
removed by glacial erosion.
Other forms of glacial erosion include polishing and plucking.
Polishing occurred where sand and silt, frozen to the glacier’s
base, slid over rock. Like sandpaper smoothing a piece of rough
wood, the rock surface becomes highly smoothed and polished.
Plucking occurred where rock fragments, fractured and loosened
from pressure exerted by the weight of the overriding glacier, were
broken off. Generally, the fragments, some as big as boulders, are
removed from the downstream side of the outcrop. In extreme cases,
the processes of abrasion and plucking can impart a whaleback
shape to an outcrop, also called a roche moutonnée. 17 Glacial Deposits
All of the deposits in the park laid down directly by or from glacial
ice are called till. Till, a nonsorted mixture of clay to bouldery-sized
material, covers the bedrock surface in most places, except the
rocky crest of Kittatinny Mountain and a few steep hillslopes.
Where it is thin, the underlying bedrock topography shows through.
Thicker till subdues and buries this irregular surface, and in many
places completely hides it. Till in the park is typically a compact,
yellowish-brown, brown, or light olive brown silty sand consisting
of a mixture of quartz sand, rock fragments, feldspar, silt, and clay.
Subangular to subrounded stones of quartz-pebble conglomerate,
quartzite, red sandstone, gray sandstone, and red shale may make
up as much as 20 percent of the deposit by volume. Many of these
are striated. This material is called lodgement till and was deposited pick
(for scale) shovel
planar beds 3 of stratified gravel and sand:
deposit of a glacial meltwater stream. basal till 1 : poorly sorted, nonstrat...
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