Once you reach this waypoint you are standing at the very last
advance of a Pleistocene Epoch glacier that occupied a major
portion of North America approximately 15 thousand years ago. At
this point in geologic time, the climate was much colder as a
massive continental glacier, known as the Laurentide Ice Sheet,
advanced downwards from Canada into and across New York State.
Imagine now the nearest beach is located close to the edge of the
present day continental shelf, beyond the visible horizon.
Moving like a giant bulldozer, this ice mass picked anything and
everything in its path from house-sized boulders to silt and clay
particles. This last particular glacier (there were possibly 5
advances) approached Staten Island from the north-northwest and
flowed to the south-southeast. As such it has been assigned on the
geologic time scale to be of Late Wisconsin age of the Quaternary
Period. The resulting line of heterogeneous debris formed a sinuous
mound, marking its final progress. This mound is called a terminal
moraine or more specifically the Harbor Hill Terminal Moraine. This
moraine continues southwestward into New Jersey and Pennsylvania
approximately adjacent to Interstate Route 80; to the northeast it
continues along the eastern margin of Staten Island across the
Narrows to Brooklyn and makes up the hilly regions along the north
shore of Long Island, and finally up into Connecticut and to Rhode
Island. Another older moraine known as the Ronkonkoma can be found
along Long Island’s south shore, but it does not exist in Staten
Island.
As the climate became slowly warmer, the glacier began to
retreat or melt faster than its forward motion. As this happened,
meltwater streams returned water to the ocean, raising sea level
approximately 300 feet to more or less its present location. The
last of this continental glacier probably melted about 12,500 years
ago. Examining the components within this mostly unsorted and
unstratified red-brown mass will determine the path that the
glacier took to arrive at its present locality. You will find many
rock and mineral specimens in place within the mound and many that
have weathered out of the moraine and tumbled onto the beach face
below. All three rocks types may be found here: sedimentary,
igneous, and metamorphic. These include sedimentary rocks from the
nearby Triassic-aged Newark Basin of the Mesozoic Era, which
consists of pieces of black shale from the Lockatong Formation,
red-brown feldspar-rich sandstone from the Stockton Formation and
fine-grained red shale from the Passaic Formation. Also, from the
Mesozoic Era and early Jurassic Period are dense chunks of grey to
rusty weathering Palisades Diabase, which is a coarse-grained and
dark-colored igneous intrusive rock that makes up the “Palisades”
cliff along the west side of the Hudson River. In addition, you
will find many mineral pebbles of black smoky quartz and
iron-stained yellow milky quartz. Metamorphic rocks found are grey
quartzite cobbles, rotten pebbles of mica-rich schist, and large
boulders of white-yellow- and grey-banded gneiss. The existence of
these rocks means they must have been exposed at the surface to the
ice’s path in order to be incorporated within the moraine. However,
this last glacial advance may have picked up and re-worked moraine
deposits from earlier glacial events here. All of this glacial
material overlies the 85 to 93 million year old Cretaceous-aged
sediments of sand and clay which are not visible at this locality,
marking a large time gap known as an unconformity or more
specifically as a disconformity where 80 million years of geology
is missing via erosion or because sediments were never deposited.
The hidden underlying Cretaceous-age formations can be found
further northeast along the beach at another earthcache locality.
This was the last of perhaps five glaciations that the New York
area had suffered in the last 2 million years. Above portions of
this moraine are finely stratified layers of silt and sand known as
glacial outwash, that were deposited by streams of glacial melt
water on its way back to the ocean. Also noticeable at the very top
of the outwash are discrete piles of discarded oyster shells
otherwise known as garbage pits or middens as archaeologists call
them. Oysters were extensively used for food by the Lenape Indians
that later occupied this area within the Raritan Bay region.
As a quick historical note, the nearby stone Conference House is
mostly composed of glacially deposited boulders and cobbles from
the moraine. If you examine the rocky components that form the
major walls of the dwelling, you will see a good representation of
the rocks found within this moraine that served as a locally
abundant source of building materials. Also examine the cement that
holds these rocks together, especially the small white chalky bits.
The abundant oyster shells from the nearby middens were ground up
and added as part of the sandy cement. The structure is the Billopp
Manor House as it is formally known, was built in 1680. It was the
site of the historic Staten Island Peace Conference. Admiral Lord
Howe, Commander of His Majesty's Atlantic Squadron, invited Ben
Franklin, John Adams, and Edward Rutledge to a 3-hour meeting that
took place on September 11, 1776. Howe’s intention was to persuade
the Colonists to return to the folds of the British Empire. His
offer included freedom from reprisal and the addition of more of
the rights enjoyed by other Englishmen. Well, its obvious today
this meeting didn’t go very well! Tours of the interior are
available.
To get credit for this Earthcache, estimate the thickness of the
moraine at the stated coordinates.