|
<
How Gravel was Formed and Transported > The
Big Chill
Written
by local author
They
term it an ice sheet. Some sheet! Twelve thousand years ago, if you
stood at its base , somewhere along present-day Route 46, and looked
up, you probably couldn’t see the top. And if air temperatures were
above freezing, the mists generated from its melting would have
shrouded its icy flanks like those of some Himalayan peak. It easily
smothered the Jenny Jump and Allamuchy Mountains and no peaks in New
Jersey rose above it. Back towards it Canadian birth place, its
thickness exceeded a mile, so the geologist say.
The
glacier that took up residence in Warren County during the Earth’s
last ice age left a lasting impression that is still evident in many
ways. This glacier was much more than ice. On it’s southward
journey. It operated like a huge bulldozer, digging into
boulder-strewn fields. Knocking the rocky tops off mountains, and
gouging out valleys as it went. Eventually the ice sheet incorporated
these boulders, rock chunks, and other debris into its mass, its
leading edge becoming more rock than ice. Thus, the glacier was like a
huge piece of very coarse sandpaper, grinding, rounding off, striating
everything it passed over.
After
the passage of thousands of years, when the glaciers reached these
somewhat warmer climes, and when global temperatures rose, the ice
gradually melted and left behind these boulders, sand, and earth in
huge ridges, marking its southernmost advance.
These
ridges are called terminal moraines, and one of these moraines crossed
our county like a “Great Wall of China” stretching from
Hackettstown to Belvidere. South of this moraine, then, was land
untouched by glacial activity; north of it, land that had been ravaged
by it.
Warren
County is a glaciologist’s dream, a perfect laboratory for studying
this last great continental ice sheet. It is called the Wisconsin
Glacier after the area where its effects are most notable. The glacier
actually began its southward and southwester movement from Labrador in
Canada, coming into creation because of global cooling caused,
probably, by the earth’s tilting away from the sun.
The
Wisconsin Ice Sheet, the last of several glaciers, came further south
and had a greater impact on Warren County than any others. It reached
it’s peak some 20,000 years ago, at a time when cave dwellers in
Europe were painting the walls of their caves with animal they saw,
some of which, the elephant-like wooly mammoths, mastadons,, and caribou,
also roamed the field and forests of Warren County.
At
this time, ice sheet covered over 4.8 million square miles of land in
North America to a thickness of many thousands of feet. So much of the
earth’s water was frozen into the ice sheet that the ocean levels
had dropped considerably. The Bering Strait between the Asian mainland
and Alaska was dry because of this, and Asian nomads could and did
walk to North America, becoming some of its earliest inhabitants. New
Jersey’s shoreline was located about 100 miles east of today’s
shore, and trawler men off our coast still pull up mastadon bones and
teeth in their nets.
But
no area in New Jersey has more reminders of the frigid past than
Warren County. After its cataclysmic arrival, the Wisconsin Ice Sheet
remained here thousands of years, long enough to have a very
significant impact. Route 46 follows the terminal moraine across the
county, almost to Belvidere, but the wide ridge is most noticeable on
the highway’s south side. Vienna’s Central School is built upon
it, and when entering Great Meadows from the east, it is obvious to
the left beyond the railroad tracks. Pio Costa’s Sand & Gravel
pit is part of it, and a good cross section of it is visible at
Neville Plaza west of Great Meadows. Further west past Hot Dog Johnnie’s,
an opening in the moraine is visible on the right, and at Bridgeville,
a left turn on Route 519 will take the observers through the middle of
a large excavated section of it.
Lakes
and former lakes are characteristic of glacial topography. The
southward movement of the ice sheet bulldozed depressions down to
bedrock. Then the ice melted, leaving the moraine as a natural dam;
water from the ice melt and other sources filled in the depressions.
In are area Budd Lake, Cranberry Lake, Sunfish Pond, Allamuchy Pond,
Mountain Lake and the lake that formerly existed in the Great Meadows
are all examples of this.
Smaller
bodies of water called kettles ponds were formed when chunks of ice,
house-sized and larger, broke off the deteriorating glacier and were
buried in the moraine. The unmelted ice might have stayed there many
years before eventually melting, leaving a large hole in the ground.
As water level rose because of the melting ice sheet, the hole or “kettle”
filled with water. Several of these kettle ponds can be seen along the
Townsbury-Barkers Mill Road; the pond of the “Pond View”
development is one. Others can be found off Bilby Road in Independence
and at other areas in Mansfields Township,
One
kettle pond off Asbury Road in Independence Township is of special
significance: it was here in 1844 that farmer Abraham Ayers, while
digging in a pond on his property, discovered the skeleton of five
mastadons. The most perfect one, almost nine feet tall, was made part
of a traveling exhibit which toured the country . Harvard University
bought it finally and it can be found today in its Museum of
Comparative Anatomy, where it is erroneously known as the Cambridge
Mastadon.
Since
the Ayers discovery, over 40 sites in the Delaware Valley have
produced mastadon remains. So common are they that they no longer
excite the scientific community, nor is there a demand for them by
museums.
The
remains of a large moose-like animal that roamed North America at the
same time, Cevalces scotti, are much rarer, the only two complete
skeletons having been found in Warren County. Castoroides, a giant
beaver weighting several hundred pounds, also roamed the area.
Certainly some of these creatures were killed by early inhabitants of
the County who moved in as the ice sheet retreated northward but most
probably died because of their inability to adapt to the warming
environment.
Great
Meadows, and the land around it, contain a variety of ice age relics.
The muckland itself is the location of a lake carved out by the
glacier and then dammed by its moraine at Vienna. One wonders how many
mastadon skeletons are buried beneath its surface. Post Island rising
out of ehe meadows here is actually a kame made from a huge piece of
glacial ice, gravel and rock-fill, left behind on top of the ground
when the glacier retreated. The ice melted, leaving this hill of
debris several acres in volume.
On
Far View Road, near the entrance to Jenny Jump Park, is a glacial
remnant called an erratic, an all limestone boulder weighing several
tons standing by itself on the south side of the road. This huge
memento was carried several hundred feet uphill by glacier and left
there when the ice melted. Another erratic, weighing an astounding
2,000 tons, rests in a field near the corner of Hope Road and Marble
Hill Road in the same area. It was carried at least a mile uphill. In
Jenny Jump Park, itself, there are many erratics, and the exposed rock
ledge along the Summit Trail shows the deep striations gouged here
20,000 years ago by the glacier. On Shades of Death Road, on the left
side heading northeast, several miles of the hillside are covered with
large limestone erratics, many the size of a house.
|