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This is the sixth in a series of my “geologic” geocaches on Staten Island, intended to educate fellow “geocachers” about the local geology. This now single-stage cache is located near the shoreline but not on it! Safely park your vehicle in the adjacent parking lot; family friendly and wheel-chair accessible cache; nice easy cache for the newbies!
Geologically speaking, the geology of this area is fairly new, but the man-made structures were installed here in 2003. The location you are standing over is the meeting place of the lithosphere, atmosphere, and the hydrosphere. Otherwise known as the beach, this is a unique locality.
Approximately 15,000 years ago, the shoreline below you was created when the last great Pleistocene continental glacier melted causing sea level to rise to more or less its present level. Prior to this time the nearest beach was about 50 miles away due east of your location and onto the continental shelf. Looking northeast from here, you will see the large and looming Verrazano Narrows Bridge between Staten Island and Brooklyn, just southeast of that point you will see 2 man-made and abandoned islands: Hoffman Island (the larger) created in 1872 and Swinburne Island created in 1875 (the smaller), and directly east, the curved sand spit of Sandy Hook, New Jersey. The latter two islands were used as a quarantine stations for immigrants prior to coming to Ellis Island.
On the lithosphere you just left, the sand is derived from three main sources. One main source is the Hudson River Estuary whose mouth is beneath the Verrazano Narrows Bridge. An estuary is a drowned river valley, formed when continental glaciers melt. Deposited here are mineral and rock fragments that the Hudson River has picked up from the physical weathering and erosion of the metamorphic Manhattan Schist and igneous Palisades Diabase lopolith. These minerals include grains of red almandine garnet, black biotite and silvery muscovite mica flakes, grey rutile, black hornblende and zircon, various feldspars, and milky quartz among others. These grains have been deposited along Staten Island’s eastern shore by a south-east flowing longshore or littoral current created by the outflow of the Hudson River through the Narrows. The second sand source is the Ordovician serpentinite bedrock. Existing 411-413 feet above sea level, runoff from this 450 million year old metamorphic ultramafic rock contributes mostly dark black and magnetic magnetite and yellow-brown limonite grains to the sand. These two minerals give the sand here its predominant brownish-yellow color. After a high tide and due to its high specific gravity, the magnetite sand sometimes becomes concentrated in long bands parallel to the shore or is found in dark black isolated patches. Many people think these are oil slicks washed upon the beach by large passing ships, but they are only harmless accumulated grains of magnetite! The third and final source of sand is the erosion of the Harbor Hill Terminal Moraine. Deposited as the last gasp of the forward motion of the Pleistocene glacier from the Cenozoic Era, this feature can be traced along the northern shore of Long Island, across the Narrows into Staten Island and generally following Hylan Boulevard southwest to its end at the Conference House and into Carteret, New Jersey. Whatever rocks and minerals the glacier picked up along its journey from Canada through portions of New York and New Jersey, are also found here. This would include tiny fragments of the Palisades Diabase lopolith, the Stockton Arkose, Storm King Granite, members of the Passaic Formation, and the Lockatong Argillite, Fordham Gneiss, and Inwood Marble. Only the most chemically resistant silicate and oxide mineral grains remain on the beach while other less resistant rock and mineral types are in the process of physical and chemical breakdown. Once you are done finding the caches below, go down to the beach, grab a handful of sand, and look for these minerals with a suitable hand lens.
Besides the geology there is a wide host of oceanography and marine biology to observe here as well. However, you will come across this information while you look for the caches! As you begin your trek, look down and you will definitely see rabbits, shore birds, pigeons, several large herons, many types of crabs, oyster shells, clam shells, lobsters, sea stars, snails, and horseshoe crabs. This small cache is a clear tube. Go to the coordinates and look for an new Altoid tin that holds small items and a log sheet. Be very aware of fishing muggles and the like, especially on a nice day! Accessing the cache may be a bit noisy, so please keep it down. Have fun and enjoy the view!
Additional Hints
(Decrypt)
Or njner bs ornpu pbzoref, gura ybbx sbe ynetre znevar yvsr, rfcrpvnyyl orybj ba gur evtug!